Metal complexes for use as dopants and other uses

ABSTRACT

The invention relates to electrochemical devices comprising complexes of cobalt comprising at least one ligand with a 5- or six membered, N-containing heteroring. The complex are useful as p- and n-dopants, as over of electrochemical devices, in particular in organic semiconductors. The complexes are further useful as over-discharge prevention and overvoltage protection agents.

TECHNICAL FIELD

The present invention relates to novel complexes of transition metals,electrochemical devices comprising the complexes and uses of thecomplexes in particular in electrochemical devices. The inventionfurther relates to methods of preparing electrochemical devices, andfurther methods.

BACKGROUND ART AND PROBLEMS SOLVED BY THE INVENTION

Chemical doping is an important strategy to alter the charge transportproperties of both molecular and polymeric organic semiconductors, andfinds application in organic electronic devices, for instance in organiclight-emitting devices (OLEDs). Various materials have been reported fortheir use as p-dopants, for example, ranging from stronglyelectron-accepting organic molecules such as2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) totransition metal oxides such as WO₃ (Meyer, J. et al., Mater. Chem.2009, 19, 702), metal organic complexes such as molybdenumtris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] (Qi, Y. et al., J.Am. Chem. Soc. 2009, 131, 12530-12531) and redox active salts such asNOBF₄ (Snaith, H. J. et al., Appl. Phys. Lett. 2006, 89, 262114) or(p-BrC₆H₄)₃NSbCl₆ (Bach, U. et al., Nature 1998, 395, 583-585. Many ofthese materials are usually applied by vacuum deposition techniques andexhibit low solubility in organic solvent, others are facing stabilityissues or are reactive and prone to side reactions.

It is thus an objective of the present invention to provide a new classof dopants that allows to easily tune the chemical, physical, opticaland/or electronic properties of the doping agent in order to carefullyadapt it to the desired application. For example, for OLEDs, doping ofinterfaces might be preferable, which is easier if the dopant isdeposited by thermal evaporation. Dopants based on metal complex havingnegatively charged ligands, for example, may be used to obtain neutralcomplexes that can be deposited by thermal evaporation. Doping atinterfaces by evaporation could be used for OLEDs, organic solar cellsand also the solid state dye-sensitized solar cells (ssDCSs).

Furthermore, it is an objective to provide dopants the solubility ofwhich can be adjusted. For example, it is an objective to providedopants that are easily soluble in organic solvents, that are stable andthat do not engage in undesired side reactions in the device. Besidesthe solubility, the dopants are ideally charged or neutral to use bythermal evaporation in organic light emitting diodes, and solar cells.

In organic light emitting diodes (OLED), one problem of dopants is theirdiffusion across the different layers of the OLED, leading to areduction in performance or even loss of function. It would thus beadvantageous to provide dopants the diffusion of which can becontrolled, for example by using suitable counter ions.

Dopants are also used in solid state (ss) dye-sensitized solar cell(DSC) applications, in which the liquid electrolyte is replaced by asolid hole transporting material (HTM). In particular when using2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene(spiro-MeOTAD) as HTM, high power conversion efficiencies have beenyielded. Bach et al. (1998) were the first to report on the use ofspiro-MeOTAD in ssDSCs and although research interest to identifycompetitive alternatives is strong, spiro-MeOTAD is still the system ofchoice when high efficiencies are demanded. Several intrinsic propertieslike its glass transition temperature, solubility, ionization potential,absorption spectrum and solid-state morphology make Spiro-MeOTAD asuitable candidate for DSC applications. However, similar to otherorganic hole conductors including liquid hole conductors, spiro-MeOTADsuffers from a relatively low conductivity in its pristine form. It isan objective to provide dopants that can also be used in liquid organiccharge transporting materials.

It is an objective of the invention to provide means for increasingconductivity of charge transporting materials, in particular of holeand/or electron transporting materials, such as, for example, organicconductors or semiconductors.

It is also an objective of the invention to provide a means to improvecharge collection and/or charge transfer, for example at the interface,in particular in case dopants are applied by evaporating the dopant.

With respect to solid state dye-sensitized solar cells (ssDSCs) it isnoted that Bach et al (1998) already employed (p-BrC₆H₄)₃NSbCl₆ as achemical p-dopant but up to the present date, no detailed study onp-type doping in dye solar cells has been reported. Surprisingly, theuse of chemically p-doped spiro-MeOTAD has gradually diminished and mostof the recent publications on spiro-MeOTAD-based ssDSCs do not followthis strategy. The reason, why high power conversion efficiencies canstill be achieved, is the device fabrication under atmosphericconditions and a facile reaction of spiro-MeOTAD with molecular oxygenunder illumination, a process referred to as photo-doping. Therefore, itis currently believed that chemical p-doping is not necessarily the keyto high performance. On the other hand, photo-doping is clearly aprocess that is not easy to control. Therefore, it is an objective ofthe present invention to provide means of increasing conductivity oforganic charge transporting materials by other and/or additional waysthan by photo doping. It is in particular an objective to increasingconductivity of organic charge transporting material in a highlyreproducible way and to fabricate stable electrochemical devices usingorganic charge transporting materials.

With respect to rechargeable batteries, such batteries are used in manyelectronic devices, in particular portable devices, such as cell phones,laptops, tablet computers (iPad, etc), portable computer game consolesand so forth, for example. Rechargeable batteries, in particularlithium-ion batteries, may experience thermal runaway resulting inoverheating. Sealed cells will sometimes explode violently. Lithium-ionbatteries can rupture, ignite or explode when exposed to hightemperature. For example, short-circuiting may cause the cell tooverheat and possibly catch fire. It is an objective of the invention toprovide ways for preventing or reducing the risk of explosion and/or therisk of over-discharging.

It is also an objective of the invention to provide agents that can beused for protecting electronic devices, in particular electrochemicaldevices against overvoltage.

The present invention addresses the problems and objectives depictedabove, which are part of the present invention.

SUMMARY OF THE INVENTION

The present inventors provide complexes of transition metal complexes,in particular of cobalt, that have several useful properties when usedin electrochemical devices. In particular, the complexes are useful asdopants in electronic hole and/or electron transport layers. It hassurprisingly been found that the complexes of the invention are suitableto increase the conductivity and charge carrier mobility of organiccharge transporting materials.

In an aspect, the invention provides a complex of formula (I):M(La)_(n)(Xb)_(m)  (I)wherein:M is a metal selected from first row transition metals, in particularcobalt, nickel, copper, and from Ru, Os, Rh, Ir, Pd, Pt, Au, and Ag;n is an integer from 1 to 6 and a is a consecutive number of a first setconsisting of the integers of 1 to n (1, . . . , n), so that there are nligands L1, . . . , Ln;m is 0 or an integer from 1 to 5 and b is a consecutive number of asecond set consisting of 0 and integers of 1 to m (0, . . . , m), sothat if m>0 there are m ligands X1, . . . , Xm;wherein n+m equal the appropriate number of ligands present on metal M;any La (L1, . . . , Ln) is independently selected from a mono-, bi-, ortridentate ligand, with the proviso that at least one of said La (L1, .. . , Ln) comprises a substituted or unsubstituted ring or ring systemcomprising a five- and/or six-membered, N-containing heteroring, saidfive- or six-membered heteroring, respectively, comprising at least onedouble bond;Xb is independently a monodentate co-ligand.

In an aspect, the present invention provides a doped charge transportingmaterial comprising an organic hole or electron transporting materialand the complex of formulae (I).

In an aspect, the present invention provides an electrochemical and/oroptoelectronic device comprising said complex of the invention.Preferably, the device is a photoelectrochemical device.

In an aspect, the present invention provides an electrochemical devicecomprising a first and a second electrode and, between said first andsecond electrode, an organic charge transport layer, said chargetransport layer comprising the complex of formula (I)

In an aspect, the present invention provides a photoelectric conversiondevice comprising a light absorption layer (3) and an electron or holeconducting, organic charge transport layer (6), said charge transportlayer comprising the complex of formula (I).

In an aspect, the present invention provides the use of the complex ofthe invention as a redox active agent of an electrochemical device.

In an aspect, the invention provides the use of complexes of theinvention as a dopant for doping an organic semiconductor, a chargeinjection layer, a hole blocker layer, an electrode material, atransport material, a memory material, or combinations comprising two ormore of the aforementioned.

In an aspect, the invention provides the use of the complex of theinvention as a dopant, in particular as a p-dopant or as an n-dopant.

In an aspect, the invention provides the use of a complex of theinvention for increasing one or more selected from conductivity, chargedensity and/or charge mobility of an organic charge transportingmaterial.

In an aspect, the invention provides the use of the complex of theinvention for increasing the conductivity of an organic semiconductor.

In an aspect, the invention provides the use of the complex of theinvention as an additive of an organic semiconductor.

In an aspect, the invention provides the use of the complex of theinvention as an overvoltage protection agent.

In an aspect, the invention provides the use of the complex of theinvention as an over-discharge prevention agent.

In an aspect, the invention provides the use of the complex of theinvention as an explosion prevention agent in rechargeable batteries.

In an aspect, the invention provides the use of the complex of theinvention in redox batteries. The complex of the invention is thususeful to improve charge collection and or charge transfer atinterfaces.

In an aspect, the invention provides the use of the complex of theinvention in layers applied by evaporation.

In an aspect, the present invention provides a method of preparing acharge transporting material, the method comprising the step ofproviding an organic charge transporting material, and, adding theretothe complex of formula (I).

In an aspect, the present invention provides a method of preparing anelectrochemical device, the method comprising the steps of providing afirst and a second electrode and providing, between said first andsecond electrode, an organic charge transporting material comprising thecomplex of formula (I).

In an aspect, the invention provides a method for doping an organiccharge transporting material, the method comprising the step of adding,to said material, the complex of formula (I).

In an aspect, the invention provides a method for increasing theconductivity of an organic semiconductor, the method comprising the stepof adding, to said semiconductor, the complex of formula (I).

In an aspect, the invention provides a method for preventingover-discharge of a rechargeable battery, the method comprising the stepof adding the complex of formula (I) to the battery.

Further aspects and embodiments of the present invention are describedbelow.

BRIEF DESCRIPTION OF THE FIGURES

In the figures,

FIG. 1 shows exemplary complexes 1-8 and their salts in accordance withthe present invention.

FIG. 2 shows the I-V characteristics of a spin-cast organic holetransporting material (Spiro-MeOTAD) to which a complex of the invention(complex 2) was added at different concentrations in the range of 1% to3.4% as shown in the figure and in accordance with an embodiment of theinvention. Doping ratios correspond to the molar percentage of complex 2that has been added to a solution of Spiro-MeOTAD.

FIG. 3 shows the conductivity extracted from IV measurements ofSpiro-MeOTAD films (FIG. 2) as function of level of doping with complex2.

FIG. 4 shows J-V characteristics of ssDSCs containing different amountsof a dopant (complex 2) in accordance with the invention, compared to adevice devoid of any dopant (Blank). Addition of the dopant inaccordance with the invention mainly increases the fill factor and thusthe performance of the device.

FIG. 5 shows J-V characteristics of a ssDSC according to a preferredembodiment of the invention, comprising 1.6% of complex 2 dopant.

FIG. 6 (FIGS. 6-1 and 6-2) shows exemplary tridentate ligands La (H-1 toH-31) based on a substituted bipyridine, which ligands may be used in acomplex in accordance with an embodiment of the invention.

FIGS. 7 (7-1 and 7-2) shows exemplary tridentate ligands La (J-1 toJ-26) based on a substituted phenantroline, which ligands may be used ina complex in accordance with an embodiment of the invention.

FIGS. 8 (8-1 and 8-2) shows exemplary tridentate ligands La (K-1 toK-33) based on a di-substituted pyridine, which ligands may be used in acomplex in accordance with an embodiment of the invention.

FIG. 9 shows exemplary tridentate ligands La (L-1 to L-4) based on adi-substituted pyrazole, imidazole or pyrrole, which ligands may be usedin a complex in accordance with an embodiment of the invention.

FIGS. 10 (10-1 and 10-2) shows exemplary ligands (M-1 to M-15) of asimilar type as those shown in FIG. 6, with additional substituentsbeing present.

FIGS. 11 (11-1 and 11-2) shows exemplary ligands (N-1 to N-20) of asimilar type as those shown in FIG. 7, with additional substituentsbeing present.

FIGS. 12 (12-1 and 12-2) shows exemplary ligands (P-1 to P-16) of asimilar type as those shown in FIG. 7, with additional substituentsbeing present.

FIGS. 13 (13-1, 13-2, 13-3, 13-4) shows exemplary bidentate ligands (Q-1to Q-63) based on substituted pyridine, pyrazole, imidazole or pyrrole,which ligands may be used in a complex in accordance with an embodimentof the invention.

FIG. 14 is a schematic representation of a DSC according to theinvention.

FIG. 15 is a schematic representation of the said light adsorption layer3 of the dive shown in FIG. 14.

FIG. 16 is a schematic representation of an embodiment of a flexibleconversion device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to complexes comprising a metal atomselected from first row transition metals and/or from metals of groups 8to 11 of the periodic table, in particular the platinum group metals(Ru, Os, Rh, Ir, Pd, Pt), Silver (Ag) and Gold (Au).

According to an embodiment, the metal atom M may thus be selectedpreferably from the metals Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Pt,Rh, Ir and Zn. Preferably, the metal M is selected from Co, Rh, Ir, Ni,Cu, Ru and Pt.

According to an embodiment, M is selected from Fe, Co, Ni, and Cu.

According to an embodiment, the complexes of the invention comprise ametal atom selected from cobalt (Co), rhodium (Rh), and iridium (Ir).Most preferably, M is cobalt (Co).

The term “comprising”, for the purpose of the present specification, isintended to mean “includes, amongst other”. It is not intended to mean“consists only of”.

As the complex of the invention may form a redox couple, the metal atomM may be present at different oxidation levels in the complex of theinvention. For example, the metal atom may be present in the +II and/or+III oxidative states. These oxidation numbers may apply, for example,if M is cobalt.

The complex comprises one or more ligands, preferably two or moreligands. According to an embodiment, the complex comprises at least oneN-containing heteroring and/or a ring system comprising at least oneN-containing heteroring. Said heteroring and/or ring system may besubstituted or unsubstituted. Preferably, the heteroring is a five- orsix-membered heteroring comprising at least one nitrogen atom andpreferably comprising at least one double bond.

According to a preferred embodiment, the complex of the inventioncomprises a structure of formula M (La)_(n)(Xb)_(m) as defined above asformula (I).

Since n may be an integer from 1 to 6, the complex of formula (I)contain at least one but possibly up to six ligands La. Accordingly, thecoordination number of the complex of the invention is preferably four(4) or six (6), meaning that there are preferably four or six donoratoms of ligands (with the preferred or according metals) that areattached to the metal (M). In other words, the ligands (La)_(n)(L1, . .. , Ln) and (Xb)_(m) (if applicable) together provide four, morepreferably six donor atoms that are bound to the metal M by a coordinatecovalent bond.

The different embodiments of the complex of formula (I) are shown belowin the case of coordination number is 6. The same applies analogously incase the coordination number is 4.

In case n is 1 and L1 is a monodentate ligand, m is 5:

(II) M L1 X1 X2 X3 X4 X5, wherein X1 to X5 may be the same or different.

In case n is 1 and L1 is a bidentate ligand (m is 4):

(III) M L1 X1 X2 X3 X4, wherein X1 to X4 may be the same or different.

In case n is 1 and L1 is a tridentate ligand (m is 3):

(IV) M L1 X1 X2 X3, wherein X1 to X3 may be the same or different.

In case n is 2 and L1 and L2 are both monodentate ligands (m is 4):

(V) M L1 L2 X1 X2 X3 X4, wherein L1 and L2 may be the same or different,and any one of X1 to X4 may be the same or different.

In case n is 2 and L1 and L2 are both bidentate ligands (m is 2):

(VI) M L1 L2 X1 X2, wherein L1 and L2 may be the same or different, andX1 and X2 may be the same or different.

In case n is 2, L1 and L2 are a mono- and a bidentate ligands,respectively (m is 3):

(VII) M L1 L2 X1 X2 X3, wherein L1 and L2 are different any one of X1 toX3 may be the same or different.

In case n is 2 and L1 and L2 are a mono- and a tridentate ligand,respectively (m is 2):

(VIII) M L1 L2 X1 X2, wherein L1 and L2 are different and any one of X1and X2 may be the same or different.

In case n is 2, L1 is a bidentate ligand and L2 is a tridentate ligand(m is 1):

(IX) M L1 L2 X1, wherein L1 and L2 are different.

In case n is 2 and L1 and L2 are both tridentate ligands (m is 0):

(X) M L1 L2, wherein L1 and L2 may be the same or different.

In case n is 3 and L1, L2 and L3 are all monodentate ligands (m is 3):

(XI) M L1 L2 L3 X1 X2 X3, wherein any one of L1 to L3 may be the same ordifferent and any one of X1 to X3 may be the same or different.

In case n is 3 and L1, L2 and L3 are all bidentate ligands (m is 0):

(XII) M L1 L2 L3, wherein any one of L1, L2 and L3 may be,independently, the same or different from any other of L1, L2, L3,respectively. For example, L1 to L3 may all be the same.

In case n is 3, L1 is a bidentate ligand and, L2 and L3 are bothmonodentate ligands (m is 2):

(XIII) M L1 L2 L3 X1 X2, wherein L1 is different from L2 and L3, L2 andL3 may be the same or different, X1 and X2 may be the same or different.

In case n is 3, L1 and L2 are both bidentate ligands and L3 ismonodentate:

(XIIIa) M L1 L2 L3 X1

In case n is 3, L1 is a tridentate ligand, L2 and L3 are bothmonodentate ligands (m is 1):

(XIV) M L1 L2 L3 X1, wherein L1 is different from L2; L3 and L2 may bethe same or different.

In case n is 3, L1 is a tridentate ligand, L2 is a bidentate ligand andL3 is a monodentate ligand (m is 0):

(XV) M L1 L2 L3, wherein L1, L2 and L3 are all different.

In case n is 4, L1 is a bidentate ligand, L2 to L4 are monodentateligands (m is 1):

(XVI) M L1 L2 L3 L4 X1, wherein L1 is different from L2 to L4; and anyone of L2 to L4 may be the same or different.

In case n is 4, L1 is a tridentate ligand, L2 to L4 are monodentateligands (m is 0):

(XVII) M L1 L2 L3 L4, wherein L1 is different from L2 to L4; and any oneof L2 to L4 may be the same or different.

In case n is 4 and L1 to L4 are all monodentate ligands (m is 2):

(XVIII) M L1 L2 L3 L4 X1 X2, wherein any one of L1 to L4 may be the sameor different and X1 and X2 may be the same or different.

In case n is 4, L1 and L2 are both bidentate ligands and L3 and L4 aremonodentate:

(XVIIIa) M L1 L2 L3 L4, wherein L1 and L2 may be the same or different,and, independently, L3 and 14 may be the same or different.

In case n is 5, L1 is a bidentate ligand and L2 to L5 are allmonodentate ligands (m is 0):

(XIX) M L1 L2 L3 L4 L5, wherein L1 is different from L2 to L5 but L2 toL5 may be the same or different.

In the other cases where n is 5 (or 6), m is 1 (or 0, respectively), L1to L5 (or L1 to L6, respectively), are all monodentate ligands, whichmay be the same or different.

From the above it becomes apparent that the complexes of the inventionmay be homoleptic (contain identical ligands La with m being 0) orheteroleptic (containing at least two different ligands).

According to an embodiment, the complex of the invention is selectedfrom the complexes of formulae (II) to (XIX) above.

Preferably, n is 1, 2 or 3, more preferably 2 or 3. If n is 2, L1 and L2are preferably identical. If n is 3, L1 to L3 are preferably identical.

According to an embodiment of the complex of the invention, n is 2 (M L1L2) or 3 (M L1, L2, L3) and m is 0 in both cases.

According to an embodiment, the complex of the invention comprises atleast 2 or at least 3 ligands La of identical structure (L1=L2 orL1=L2=L3, respectively).

According to an embodiment, the complex of the invention is overallneutral, or carries an overall positive or negative charge. As can beseen from the ligands of the invention as detailed elsewhere in thisspecification, the charge of the entire complex can be adjusted to beneutral or even negatively charged, in the oxidized or reduced state, asdesired, by selecting appropriate negatively charged ligands. For thepurpose of the present specification it is considered to be advantageousto be capable of adjusting the charge of the complex, in order to adjustsaid charge in dependency of other constituents of the electrochemicaldevice of the invention. In particular, the charge of complex can beadjusted to be neutral or negatively charged, so as to avoidelectrostatic interactions with other constituents of theelectrochemical device.

Herein below, preferred embodiments of the at least one ligand in thecomplex of the invention are given, said ligand comprising a substitutedor unsubstituted ring or ring system comprising a five-memberedheteroring and/or a six-membered heteroring. These embodiments alsoapply for the ligands La (L1, . . . Ln) of the complex of formula (I).

The five- or six membered, N-containing heteroring may be, independentlyprovided as an unsubstituted or substituted heteroring. The heteroringmay be fused to another ring or ring system, and/or two substituentsof/on a carbon of the heteroring may form a ring, which may result in aspiro compound in which one of the rings is said five- or six memberedheteroring. Furthermore, the five- or six membered heteroring may beconnected by a covalent bond to another ring or ring system, for exampleto a pyridine ring or to a polycyclic system containing one or morepyridine rings.

Preferably, said substituted or unsubstituted five- or six membered,N-containing heteroring comprises at least one double bond. According toan embodiment, the five- or six membered heteroring comprises at leasttwo double bonds. According to an embodiment, the five- or six memberedheteroring is preferably aromatic.

According to a preferred embodiment, the complex of the inventioncomprises at least one, more preferably at least two, even morepreferably at least three bidentate ligands La, which may be the same ordifferent.

According to another, still more preferred embodiment, the complex ofthe invention comprises at least one, preferably at least two tridentateligands La, which may be the same or different.

According to an embodiment, at least one of said n ligands La (L1, . . ., Ln) comprises a pyridine ring (six-membered, N-containing heteroring)or a ring system comprising a pyridine ring connected by a covalentsingle bond or fused to a further heteroring, which may be five- and/orto a six-membered, wherein said pyridine ring or a ring systemcomprising a pyridine ring and said further heteroring, independently,may or may not be further substituted.

According to an embodiment, said further five- or six memberedheteroring comprises at least one heteroatom selected from the group ofN, O, P and S, preferably at least one N.

According to an embodiment, if said ligand La comprises a five-memberedheteroring, said five-membered, N-containing heteroring comprises two ormore (preferably up to 4) heteroatoms. Preferably, at least a firstheteroatom is nitrogen, and at least a second heteroatom or furtherheteroatom is/are selected, independently, from N, O, P and S.Preferably, said second heteroatom is N, and, if applicable, furtherheteroatoms (the third, fourth, etc.) are selected independently, fromN, O, P and S, preferably they are N.

According to an embodiment, any La (L1, . . . , Ln) ligand isindependently selected from substituted and unsubstituted pyridine orpolypyridine, substituted and unsubstituted pyrazole, substituted andunsubstituted pyrazine, substituted and unsubstituted triazole,substituted and unsubstituted pyridazine, substituted and unsubstitutedimidazole; wherein substituents are independently selected fromhydrocarbons comprising 1 to 40 carbons and 0 to 20 heteroatoms,halogen, (—F, —Cl, —Br, —I), —NO₂, —NH₂ and —OH.

According to an embodiment, any one of said n ligands La (L1, . . . ,Ln) is, independently, selected from compounds of formulae (1)-(63)below:

wherein:any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, if applicable/if present, maybe selected, independently, from H and from hydrocarbons comprising 1 to40 carbons and 0 to 20 heteroatoms; R′ and R″ are selected,independently from substituents —CH₂R¹, —CHR¹R² and —CR¹R²R³.

For the purpose of this specification, the expressions “if applicable”and “if present”, which are generally preceded by a list or range ofsubstituents (e.g. R¹-R⁸) and followed by a definition of substituentsin terms of chemical names (e.g. hydrocarbon, halogen, aryl, alkyl,etc.) are intended to mean that the definition applies only is as a faras and to the extent that a given substituent of the list or range isindeed present on the specific structure formula that is referred to.Substituents of the list that are not present on the formula referred tomay be ignored (e.g. compound (I) lacks substituents R⁶, R⁷, and R⁸,which means that the definition given above applies only to thesubstituents that are present (substituents R¹ to R⁵ in compound (I)).

According to an embodiment, one or more of said substituents R¹, R², R³,R⁴, R⁵, R⁶, R⁷, R⁸, if applicable, is selected, independently, from asubstituent of formula (A-1) to (G-2) below:

wherein:the dotted line represents the bond connecting the substituent of (A-1)to (G-2) on the compound of formula (1)-(63); and,substituents R₁, R₂, R₃, R₄, R₅, R₆, and R₇, in as far as present, areindependently selected from H and from hydrocarbons comprising 1 to 30carbons and 0 to 15 heteroatoms.

According to an embodiment, at least one of said ligands La (L1, . . . ,Ln) is, independently, selected from compounds of formulae (1-2) to(3-2) below:

wherein:at least one substituent of the substituents R¹, R³, R⁵, R⁶, R⁸ isselected from the substituents (A-1) to (G-2) as defined elsewhere inthis specification. In other words, with respect to ligand (1-2), one,two or three of the group of R¹, R³, R⁵ is selected independently fromthe substituents (A-1) to (G-2) shown above.

According to an embodiment, at least one of said ligands La (L1, . . . ,Ln) is, independently, selected from compounds of formulae (1-3) to(3-3) below:

wherein, said ligand comprises at least one substituent R¹, R⁵, and/orR⁸, as applicable, selected independently from the substituents (A-1) to(G-2) as elsewhere in this specification.

According to an embodiment, any one or at least one of said ligands Lais selected independently from the compounds of formula (1-5) to (3-5)below:

wherein R¹ is selected from the substituents (A-1) to (G-2) as disclosedelsewhere in this specification.

In accordance with the present invention, it was surprisingly found thatthe presence of a second heteroatom in the ring binding to the metalatom of the complex of the invention is suitable to positively affectthe properties and suitability of the complex of the invention as aredox couple.

Therefore, ligands (e.g. La) comprising a ring with at least two ringheteroatoms are particularly preferred. According to this embodiment(“embodiment A”), the complex of the present invention comprises one ormore ligands selected from: (10)-(42), (50)-(63), and, more preferably,from complexes comprising the ligands (1), (2), (3), (4), (1-2), (2-2),(3-2), (1-3), (2-3), (3-3), (1-4), (2-4), (3-4), in as far as thesecompounds comprise at least one substituent selected from: (B-1) to(B-27), (C-1) to (C-27), (D-1) to (D-3), (F-1) to (F-10), (G-1) and(G-2).

According to another embodiment (“embodiment A”), ligands (e.g. La)comprising a ring with exactly two ring heteroatoms are particularlypreferred.

According to an embodiment (“embodiment B”), ligands (e.g. La)comprising at least two adjacent ring heteroatoms are particularlypreferred. Accordingly, the complex of the present invention comprisesone or more ligands selected from: (13), (15), (16), (17), (18), (23) to(34), (40) to (42), (50) to (54), (60) to (63), and, more preferably,from complexes comprising the ligands (1), (2), (3), (4), (1-2), (2-2),(3-2), (1-3), (2-3), (3-3), (1-4), (2-4), (3-4), in as far as thesecompounds comprise at least one substituent selected from (B-1), (B-4),(B-6), (B-8), (B-13), (B-24), (B-25), (B-27), (C-1) to (C-8), (C9) to(C-16), (C-18) to (C-27), (D-1) to D-3), (F-1), F-3), (F-4), (F-6),(G-1), (G-2).

According to an embodiment (“embodiment C”), ligands (e.g. La)comprising a five-membered heteroring are particularly preferred.Accordingly, the complex of the present invention comprises one or moreligands selected from: (6) to (34), (43) to (63), and, more preferably,from complexes comprising the ligands (1), (2), (3), (4), (1-2), (2-2),(3-2), (1-3), (2-3), (3-3), (1-4), (2-4), (3-4), in as far as thesecompounds comprise at least one substituent selected from (A-1) to(A-6), (B-1) to (B-18), (C-1) to (C-8), (D-1) to (D-3), (E-1) to (E-3),(F-1) to (F-10), (G-1) and (G-2).

According to an embodiment (“embodiment D”), ligands (e.g. La)comprising a five-membered heteroring that is not fused to any furtherring are particularly preferred.

Accordingly, the complex of the present invention comprises one or moreligands selected from: (6) to (34), and, more preferably, from complexescomprising the ligands (1), (2), (3), (4), (1-2), (2-2), (3-2), (1-3),(2-3), (3-3), (1-4), (2-4), (3-4), in as far as these compounds compriseat least one substituent selected from (A-1) to (A-6), (B-1) to (B-18),(C-1) to (C-8), (D-1) and to (D-3).

According to an embodiment (“embodiment E”), ligands (e.g. La)comprising a five- or six-membered heteroring having aromatic properties(being aromatic) are particularly preferred. Accordingly, the complex ofthe present invention comprises one or more ligands selected from: (1)to (5), (6), (7), (10) to (12), (15), (16), (19), (21), (23) to (28),(31) to (34), (35) to (36), (39), (42), (43) to (48), (50) to (53), (55)to (56), (58) to (60) and (62), and, more preferably, from complexescomprising the ligands (1), (2), (3), (4), (1-2), (2-2), (3-2), (1-3),(2-3), (3-3), (1-4), (2-4), (3-4), in as far as these compounds compriseat least one substituent selected from: (A-1) to (G-2).

According to an embodiment (“embodiment F”), the invention providescomplexes comprising one or more bi- or tridentate ligands (e.g. La)containing at least one pyridine ring and at least one substituent,wherein said substituent is bound by way of a carbon-nitrogen bond tosaid pyridine ring. Preferably, the present invention provides complexescomprising one or more ligands of formula (1), (2), (3), (4), (1-2),(2-2), (3-2), (1-3), (2-3), (3-3), (1-4), (2-4), and/or (3-4), whereinsaid ligands contain one or more substituents selected from: (A-3),(B-8) to (B-10), (B-23), (B-24), (C-4) to (C-6), (C-9) to (C-16),(C-23), (C-26), (D-2), (E-3), (F-3), (F-4), (F-7), (G-1).

According to an embodiment (“embodiment G”), the complex of theinvention comprises one or more bi- or tridentate ligands (e.g. La)comprising at least one pyridine ring and at least one substituentselected from substituents (A-1) to (A-6), (B-1) to (B-27), (C-1) to(C-27), (D-1) to (D-3), (E-1) to (E-3), (F-1) to (F-19) and (G-1) to(G-2).

The above embodiments A to G may be combined with each in as far aspossible in order to provide more specifically preferred embodiments.For example, according to a preferred embodiment, the complex comprise aligand selected from compounds that meets the definition of two or moreof embodiments A to G (the cut-set, overlap or intersection n). Forexample, the complex of the invention comprises a ligand selected fromligands comprising a five-membered heteroring and which ligand has, atthe same time, aromatic properties (the overlap of embodiments C and E).

Further particularly preferred embodiments are the overlap ofembodiments A and B; A and C; A and D; A and E; A and F. Furtherpreferred embodiments are provided by the overlap of embodiments B andC; B and E; B and F, B and G; B and F. Further preferred embodiments arethe overlap of embodiments C and D; C and E; C and F; C and G. Furtherpreferred embodiments are the overlap of embodiments D and E; D and F; Dand G. Further preferred embodiments are the overlap of embodiments Eand F; E and G. A further preferred embodiment is the overlap ofembodiments F and G.

Further preferred embodiments are provided by the overlap of threeembodiments selected from embodiments A to G. Such specificallypreferred embodiments are provided by the following overlaps ofembodiments: A, B and C; A, B and D; A, B, and E; A, B and F; A, B andG; A, C and D; A, C and E; A, C and F; A, C and G; A, D and E; A, D andF; A, D and G; A, E and F; A, E and F; B, C and D; B, C and E; B, C andF; B, C and G; B, D, and E; B, D and F; B, D and G; B, E and F; B, E andG; B, F and G; C, D and E; C, D and F; C, D and G; C, E and F; C, E andG; C, F and G; D, E and F; D, F and G.

For example, the overlap of embodiments A, B and C (underlined above)relates to complexes of the invention comprising a ligand having afive-membered ring (C) containing at least two (A) adjacent (B)heteroatoms. These ligands are those represented by compounds (13), (15)to (18), (23) to (34), (50) to (54), (60) to (63), and preferably thecompounds of formulae (1) to (5), (1-2), (2-2), (3-2), (1-3), (2-3),(3-3), (1-4), (2-4), (3-4), in as far as these latter compounds compriseat least one substituent selected from the substituents (B-1), (B-4),(B-6), (B-8), (B-13), (C-1) to (C-8), (D-1) to (D3), (F-1), (F-3),(F-4), (F-6), (G-1), (G-2).

Further preferred embodiments are provided by the overlap of fourembodiments selected from embodiments A to G. Such specificallypreferred embodiments are provided by the following overlaps ofembodiments: A, B, C, and D; A, B, C, and E; A, B, C, and F; A, B, C andG; A, B, D, and E; A, B, D and F; A, B, D and G; A, C, D and E; A, C, Dand F; A, C, D and G; A, C, E and F; A, C, E and G; A, D, E and F; A, D,E and G; A, E, F and G; B, C, D and E; B, C, D and F; B, C, D and G; B,C, E and F; B, C, E and G; B, C, F and G; B, D, E and F; B, D, E and G;B, E, F and G; C, D, E and F; C, D, E and G; C, D, F and G; D, E, F andG.

For example, an overlap of embodiments, A, B, C, and G (underlinedabove), relates to complexes of the invention comprising a bi- ortridentate ligand (La) comprising at least one pyridine ring (G), and asubstituent having a five-membered ring (C) containing at least two (A)adjacent (B) heteroatoms. Preferred ligands of this embodiment are thoserepresented by compounds of formulae (1) to (5), (1-2), (2-2), (3-2),(1-3), (2-3), (3-3), (1-4), (2-4), (3-4), in as far as these lattercompounds comprise at least one substituent selected from thesubstituents (B-1), (B-4), (B-6), (B-8), (B-13), (C-1) to (C-8), (D-1)to (D3), (F-1), (F-3), (F-4), (F-6), (G-1), (G-2).

In the embodiments and the preferred, combined or particular embodimentsabove, embodiment A may be replaced by embodiment A′, resulting in thecorresponding overlaps in which a ring with exactly two ring heteroatomsis present.

It is further noted that heteroatoms are as defined above, but nitrogenbeing the preferred ring-heteroatom. According to an embodiment, whenthere are exactly two or more than two ring-heteroatoms, saidheteroatoms are preferably nitrogen atoms.

As can be noted from the preferred embodiments specified above,substituted and unsubstituted ligands comprising a compound of any oneof formulae (1) to (5) are preferred. Still more preferred areembodiments wherein La is selected from substituted and unsubstitutedligands of formulae (1), (2) and (3).

According to an embodiment, at least one, at least two, in case ofbidentate ligands, three ligands La is/are selected independently fromthe compounds shown in FIGS. 6, 7, 8, 9, 10, 11, 12 and/or 13.Accordingly, one, two or more ligands La may be independently selectedfrom any one of ligands H-1 to H-31, J-1 to J-26, K-1 to K-33, L-1 toL-4, M-1 to M-15, N-1 to N-20, P-1 to P16, Q-1 to Q-63.

According to an embodiment, in compounds H-1 to H-31, J-1 to J-26, K-1to K-33, L1 to L4, Q-1 to Q-26, Q-43 to Q-51, any one, more than one orall available hydrogen may independently be replaced by a substituentother than H as defined above for R¹ to R⁸, and/or R₁, to R₇, as well asthe preferred embodiments of R¹ to R⁸, and R₁, to R₇ that are other thanH. It is noted that in the other exemplary ligands (M−1 to M-15, N-1 toN-20, P-1 to P-16, Q-27 to Q-42 and Q-52 to Q-63) shown in the figures,substituents replacing available hydrogens are already present, theselatter exemplary ligands thus form specific examples ofligands/compounds comprising such hydrogen replacing substituents.

Furthermore, in several of the ligands shown in FIGS. 5 to 12, methylsubstituents on nitrogen atoms corresponding to R′ and R″ as definedelsewhere in this specification are present (for example, H-2, H-4, H-6,H-8, etc). These N-methyl substituents may, according to an embodiment,be replaced by other substituents as defined for R′ and R″ elsewhere inthis specification. R′ and R″ may in particular be selected from C1-C5alkyl substituents.

According to an embodiment, in compounds H-1 to H-31, J-1 to J-26, K-1to K-33, L1 to L4, Q-1 to Q-26, Q-43 to Q-51, any one, more than one orall available hydrogen may independently be replaced by —F, —Cl, —Br,—I, (halogen), —NO₂, —CN, —OH, —CF₃, substituted or unsubstituted C1-C30alkyl, C2-C30 alkenyl, C2-C30 alkynyl, and C5 to C30 aryl as definedelsewhere in this specification for R¹ to R⁸, and/or R₁, to R₇, as wellas the preferred embodiments of R¹ to R⁸, and R₁, to R₇ that are otherthan H.

In particular in any ligand La selected from compounds H-1 to H-31, J-1to J-26, K-1 to K-33, L1 to L4, Q-1 to Q-26, Q-43 to Q-51, any one, morethan one or all available hydrogen may independently be replaced byhalogen, —CN, C1-C6 alkyls, C2-C6 alkenyls C2-C6 alkynyls, and C6-C10aryls, wherein in said alkyls, alkenyls, alkynyls and aryls one, severalor all available hydrogen may be replaced by halogen, —CN and —CF₃.

More preferably, in any ligand La selected from compounds H-1 to H-31,J-1 to J-26, K-1 to K-33, L1 to L4, Q-1 to Q-26, Q-43 to Q-51, any one,more than one or all available hydrogen may independently be replaced byhalogen, —CN, C1-C4 alkyl, wherein in said alkyl one, several or allavailable hydrogen may be replaced by halogen, —CN and —CF₃.

According to an embodiment, the complex of the invention comprises atleast one ligand (La) selected from the compounds of any one of formula(1), (2), (3), (1-2), (2-2), (3-2), (1-3), (2-3), (3-3), (1-4), (2-4),(3-4), said compound being substituted with one, or, if applicable, twoor three substituents, of formulae B-8, the other substituents beingselected as specified above, but preferably from H, halogen, —CN, —CF₃,and C1-C4 alkyls, C2-C4 alkenyls and C2-C4 alkynyls, wherein in saidalkyls, alkenyls and alkynyls one, several or all available hydrogen maybe replaced by halogen.

According to a preferred embodiment, any one of said La is independentlyselected from any one of compounds of formula (2), (3), (64), (65),(66), and (67), below:

wherein any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹ ifapplicable, is independently selected from H and from hydrocarbonscomprising 1 to 20 carbons and 0 to 15 heteroatoms, halogen, (—F, —Cl,—Br, —I), —NO₂, —NH₂, and —OH.

Further exemplary ligands La are disclosed in FIGS. 5 to 12 of theco-pending European patent applications EP11156029.8, filed on Feb. 25,2011, EP11161739.5, filed on Apr. 8, 2011. The ligands disclosed inthese applications (H-1 to H-31, J-1 to J-26, K-1 to K-33, L-1 to L-4,M-1 to M-15, N-1 to N-20, P-1 to P16, Q-1 to Q-63) and their possiblesubstituents, as disclosed on page 28-30 of the co-pending applicationare totally and entirely incorporated herein by reference.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, and of R₁, R₂, R₃, R₄, R₅, and R₆, in as far as therespective substituent is present on the compounds (1) to (67) and theirsubstituents, may thus be independently selected from H, halogen, —NO₂,—OH, —NH₂ and from hydrocarbons comprising 1 to 30 carbons and 0 to 15heteroatoms (in the case of R¹-R¹¹) or from hydrocarbons comprising 1 to20 carbons and 0 to 15 heteroatoms (in the case of R₁-R₆).

According to another embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷,R⁸, R⁹, R¹⁰, R¹¹, and of R₁, R₂, R₃, R₄, R₅, and R₆, in as far as therespective substituent is present on the compounds (1) to (67) and theirsubstituents, may thus be independently selected from H, halogen, —NO₂,—OH, —NH₂ and from hydrocarbons comprising 1 to 20 carbons and 0 to 15heteroatoms.

Heteroatoms are preferably selected, independently, from Si, N, P, As,O, S, Se halogen (in particular F, Cl, Br and I), B, Be; more preferablyfrom Si, N, P, O, S, and halogen, most preferably from N, O, S andhalogen.

According to an embodiment, any one of said substituents R¹, R², R³, R⁴,R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, and of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, andR₉ may be independently selected from the substituents of formulae (A-1)to (G-2) (applicable to R¹-R¹¹), H, halogen (—F, —Cl, —Br, —I), —NO₂,—CN, —OH, —CF₃, substituted or unsubstituted C1-C20 alkyl, C2-C20alkenyl, C2-C20 alkynyl, and C4 to C20 aryl; wherein, in saidsubstituted or unsubstituted alkyl, alkenyl, alkynyl or aryl, anyhydrocarbon group (preferably and if applicable: non adjacenthydrocarbon group) may be replaced by any one selected from the group of—O—, —S—, —S(═O)—, —S(═O)₂—, —Si—, —Ge—, —NR^(A)—, —N═, —BR^(A)—,—PR^(A)—, —P(═O)R^(A)—, —P(═O)OR^(A)—, —C(═O)—, —C(═S)—, —C(═O)O—,—OC(═O)—, —C(═NR^(A))—, —C═NR^(A)—, —NR^(A)C(═O)—, —C(═O)NR^(A)—,—NR^(A)C(═S)— and —C(═S)NR^(A)—;

wherein, if said alkyl, alkenyl, alkynyl and aryl are substituted, thesubstituents, may, independently, be selected from halogen, —F, —Cl,—Br, —I, —NO₂, —CN, —OH, —CF₃, substituted or unsubstituted C1-C15alkyl, C2-C15 alkenyl, C2-C15 alkynyl C2-C15 alkynyl, C4 to C18 aryl,wherein any hydrocarbon group of said substituent may be replaced by anyone selected from the group of —O—, —S—, —S(═O)—, —S(═O)₂—, —Si—, —Ge—,—NR^(B)—, —N═, —BR^(B)—, —PR^(B)—, —P(═O)R^(B)—, —P(═O)OR^(B)—, —C(═O)—,—C(═S)—, —C(═O)O—, —OC(═O)—, —C(═NR^(B))—, —C═NR^(B)—, —NR^(B)C(═O)—,—C(═O)NR^(B)—, —NR^(B)C(═S)— and —C(═S)NR^(B)—;wherein, if said alkyl, alkenyl, alkynyl or aryl substituent is furthersubstituted, the substituents of said substituents, if present, may beselected from halogen, —F, —Cl, —Br, —I, —NO₂, —CN, —OH, —CF₃,substituted or unsubstituted C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl,C5 to C8 aryl, wherein any hydrocarbon group of said substituent may bereplaced by any one selected from the group of —O—, —S—, —S(═O)—,—S(═O)₂—, —Si—, —Ge—, —N═, —C(═O)—, —C(═S)—, —C(═O)O—, —OC(═O)—. Furthersubstituents of said further substituents are preferably selected fromhalogen, —CN and C1 to C4 alkyl, C2-C4 alkenyl and C2-C4 alkynyl,wherein any available hydrogen of said alkyl, alkenyl or alkynyl may besubstituted by halogen.

R^(A) may be selected from H and from substituted or unsubstitutedC1-C15 alkyl, C2-C15 alkenyl, C2-C15 alkynyl C2-C15 alkynyl, C4 to C18aryl as defined above (including replacement groups). Preferably, R^(A)is selected from H, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C4-C10aryl, —CN, wherein said alkyl, alkenyl, alkynyl and/or aryl may befurther substituted with —CN, C1-C4 alkyl (partially or totallyhalogenated) and halogen. More preferably, R^(A) is selected from H,—CN, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C4 to C6 aryl, which maybe further substituted by —CN or halogen.

R^(B) may be selected from H and from substituted or unsubstituted C1-C8alkyl, C2-C8 alkenyl, C2-C8 alkynyl, C5-C8 aryl as defined above(including replacement groups). Preferably, R^(B) is selected from H, H,C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C4-C6 aryl, —CN, wherein saidalkyl, alkenyl, alkynyl and/or aryl may be further substituted with —CN,C1-C4 alkyl (partially or totally halogenated) and halogen. Morepreferably, R^(B) is selected from H, —CN, C1-C4 alkyl, C2-C4 alkenyl,C2-C4 alkynyl, C4 to C6 aryl, which may be further substituted by —CN orhalogen.

According to an embodiment, any one of R_(A), R_(B) and R_(C) isindependently selected from substituents as defined for R^(A),preferably R^(B) as defined elsewhere in this specification, includingpreferred embodiments of said substituents R^(A), preferably R^(B).

For the purpose of the present specification, any alkyl, alkenyl oralkynyl specified herein may be linear, branched and/or cyclic. In thiscase, the alkyl, alkenyl and alkynyl has three or more (for example upto 30) carbons, as indicated. Any aryl having 4 or 5 carbons has anappropriate number of ring heteroatoms in order to provide an aromaticsubstituent ring. The expression “aryl” thus encompasses heteroaryls.According to an embodiment, an aryl is selected from heteroaryls andfrom aryls lacking any heteroatom.

According to a preferred embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶,R⁷, R⁸, R⁹, R¹⁰, and R¹¹, in as far as present on the compounds (1) to(67), for example, may independently be selected from the substituentsof formulae (A-1) to (G-2), H, halogen, —NO₂, and from hydrocarbonscomprising 1 to 20 carbons and 0 to 10 heteroatoms; preferably from Hand C1 to C10 hydrocarbons comprising 0 to 10 heteroaotms; morepreferably from H and C1 to C5 hydrocarbons comprising 0 to 5heteroatoms.

According to a preferred embodiment, any one of R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, and R₉ in as far as present on the substituents (A-1) to (G-2)above or on ligands, such as ligands Xb, for example, may beindependently selected from H, halogen, —NO₂ and from hydrocarbonscomprising 1 to 15 carbons and 0 to 10 heteroatoms; preferably from Hand C1 to C10 hydrocarbons comprising 0 to 10 heteroaotms; more frompreferably H and C1 to C5 hydrocarbons comprising 0 to 5 heteroatoms.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R′ and R″, ifapplicable, is selected independently from the substituents of formulae(A-1) to (G-2) (only applicable to R¹-R¹¹), H, and from C1-C10 alkyls,C2-C10 alkenyls C2-C10 alkynyls, and C5-C12 aryls (preferably C6-C12aryls), wherein in said alkyls, alkenyls, alkynyls and aryls one,several or all available hydrogen may be replaced by halogen and/or by—CN, wherein any one of said R¹ to R¹² and R₁ to R₆ may further beselected from halogen, —C≡N(—CN), —NO₂. Said aryl may or may not befurther substituted by C1-C4 alkyl, halogen and —CN.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R′ and R″, in as faras present, is selected independently from the substituents of formulae(A-1) to (G-2) (in the case of R¹-R¹¹), H, and from C1-C6 alkyls, C2-C6alkenyls C2-C6 alkynyls, and C6-C10 aryls, wherein in said alkyls,alkenyls, alkynyls and aryls one, several or all available hydrogen maybe replaced by halogen and/or —CN, wherein any one of said R¹ to R¹¹ andR₁ to R₆ may further be selected from halogen and from —C≡N(—CN). Saidaryl may or may not be further substituted by C1-C4 alkyl, halogen and—CN.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R′ and R″, in as faras present, is selected independently, from the substituents of formulae(A-1) to (G-2) (in the case of R¹-R¹¹), H, and from C1-C6, preferablyC1-C4, more preferably C1-C3 alkyl, said alkyl, being optionallypartially or totally substituted by halogen, wherein any one of said R¹to R¹² and R₁ to R₆ may further be selected from halogen and from —C≡N.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, in as far as present,is selected, independently, from the substituents of formulae (A-1) to(G-2) (this only applies to R¹-R¹¹), H, halogen, —CN and from C1-C6,preferably C1-C4 and most preferably C1-C3 alkyl, said alkyl beingpossibly substituted by halogen.

According to an embodiment, R′ and R″ are selected independently from Hand from C1-C6 linear branched or cyclic alkyl, said alkyl beingpossibly and optionally partially or totally substituted by halogen.

According to an embodiment, R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰,R¹¹, in as far as present, are selected independently from thesubstituents of formulae (A-1) to (G-2), H, halogen, —CN, and from C1-C6alkyl and alkenyl, wherein any available hydrogen of said alkyl andalkenyl may or may not be replaced by halogen and/or —CN. Preferably,R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, in as far as present, areselected independently from H, halogen, —CN, and from C1-C4 alkyl, saidalkyl being optionally totally or partially halogenated. Preferably, R¹,R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, in as far as present, areselected independently from H, halogen, —CN, —CF3 and C1-C3 alkyl.

According to an embodiment, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, in asfar as present, are selected independently from H, halogen, —CN, andfrom C1-C6 alkyl and alkenyl, wherein any available hydrogen of saidalkyl and alkenyl may or may not be replaced by halogen and/or —CN.Preferably, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, in as far as present,are selected independently from H, halogen, —CN, and from C1-C4 alkyl,said alkyl being optionally totally or partially halogenated.Preferably, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, in as far as present,are selected independently from H, halogen, —CN, —CF₃ and C1-C4 alkyl.R₇-R₉ are preferably not selected from halogen and/or CN.

Substituents R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R₁, R₂, R₃,R₄, R₅, R₆, R₇, R₈, R₉, other than H are suitable to adjust theoxidation potential of the metal complex. Without wishing to be bound bytheory, it is believed that such substituents can help obtainingelectrochemical devices, in particular DSCs, with higher V_(OC) values,and to adjust the oxidation potential of the redox couple to theproperties of the dye.

The redox-active compound may comprise one or more co- and/or spectatorligands, such as one or more ligands Xb in accordance with the complexof formula (I), for example. The spectator ligands Xb may beindependently selected, for example, from H₂O, Cl⁻, Br⁻, I⁻, CN, NCO,NCS, NCSe, NH₃, NR₇R₈R₉, and PR₇R₈R₉, wherein R₇, R₈, and R₉ areselected independently from substituted or unsubstituted alkyl, alkenyl,alkynyl and aryl. According to an embodiment, said alkyl, alkenyl andaryl is independently selected from substituted or unsubstituted C1-C20alkyl, C2-C20 alkenyl, C2-C20 alkynyl, and C4 to C20 aryl as definedelsewhere in this specification, and preferred embodiments of alkyl,alkenyl, alkynyl and aryl as defined for R¹-R¹¹ and/or R₁-R₆ elsewherein this specification. Furthermore, two or all three of R₇, R₈, and R₉may connected with each other so as to provide a cyclic or polycyclicligand.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R′ and R″, ifapplicable, is selected independently from the substituents of formulae(A-1) to (G-2) (only applicable to R¹-R¹¹), H, and from C1-C10 alkyls,C2-C10 alkenyls C2-C10 alkynyls, and C5-C12 aryls (preferably C6-C12aryls), wherein in said alkyls, alkenyls, alkynyls and aryls one,several or all available hydrogen may be replaced by halogen and/or by—CN, wherein any one of said R¹ to R¹² and R₁ to R₆ may further beselected from halogen, —C≡N(—CN), —NO₂. Said aryl may or may not befurther substituted by C1-C4 alkyl, halogen and —CN.

According to an embodiment, any one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰, R¹¹, R₁, R₂, R₃, R₄, R₅, R₆, R′ and R″, if applicable, isselected independently from H, and from C1-C10 alkyls, C2-C10 alkenylsC2-C10 alkynyls, and C5-C12 aryls (preferably C6-C12 aryls), wherein insaid alkyls, alkenyls, alkynyls and aryls one, several or all availablehydrogen may be replaced by halogen and/or by —CN, wherein any one ofsaid R¹ to R⁸ and R₁ to R₆ may further be selected from halogen and from—C≡N(—CN).

According to a preferred embodiment, any one of R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, and R₉ in as far as present on the substituents (A-1) to (G-2)above or on ligands, such as ligands Xb, for example, may beindependently selected from H, halogen, —NO₂ and from hydrocarbonscomprising 1 to 15 carbons and 0 to 10 heteroatoms; preferably from Hand C1 to C10 hydrocarbons comprising 0 to 10 heteroaotms; more frompreferably H and C1 to C5 hydrocarbons comprising 0 to 5 heteroatoms.

According to an embodiment, any one of R₁, R₂, R₃, R₄, R₅, R₆ isselected independently from H, halogen, C1-C6 linear alkyl, C3-C6branched or cyclic alkyl, and —C≡N, wherein any one of said linear,branched or cyclic alkyl may be totally or partially halogenated, andmay in particular also be —CF₃.

Other ligands of the complex of the invention, in particular ligands Xb(X1, . . . , Xm) of the complex of formula (I), may, for example, beselected from: H₂O, Cl⁻, Br⁻, I⁻, CN⁻, NCO⁻, NCS⁻, NCSe⁻, NH₃, CO, PR3(R is independently selected from substituted and unsubstituted C6-C18,preferably C6-C12 aryl and/or aroxyl (for example phenyl or phenoxyl);substituted and unsubstituted C1-C18, preferably C1-10, more preferablyC1-C4 alkyl and/or alkoxyl; imidazole, substituted imidazoles;pyridines, substituted pyridines; pyrazoles, substituted pyrazoles;triazoles; pyrazine; for example. Preferably, the ligands Xb (X1, . . ., Xm) are selected from H₂O, Cl⁻, Br⁻, I⁻, CN⁻, NCO⁻, NCS⁻, NCSe⁻, NH₃,CO, and PR3 (R is as above, preferably independently selected fromphenyl, phenoxyl, alkyl and alkoxyl).

The complex of the invention may be charged or uncharged, in dependenceof the charge of the ligand. Preferably, the complex is cationic. Inthis case, the complex is preferably provided together with a suitableanionic species. The anion may be chosen in dependence of the specificdevice or material, to which the complex is to be added. The anion maybe chosen, for example in OLED applications, so as to limit migration ofthe complex, for example to another layer. Accordingly, the inventionprovides a salt comprising the complex of the invention and an anionicspecies.

The anionic species may be an organic or an inorganic anion.

According to an embodiment, the anion is selected from the groupconsisting of halogen (in particular Cl⁻, Br⁻, I⁻), CN⁻, NCO⁻, NCS⁻,NCSe⁻, ClO₄ ⁻ (perchlorate), PF₆ (hexafluorophosphate), BF₄(tetrafluoroborate), B(CN)₄ (tetracyanoborate), CF₃SO₃(trifluoromethanesulfonate, triflate), (CF₃SO₂)₂N(Bis(trifluoromethane)sulfonamide, TFSI), B(C₆H₃(m-CF₃)₂)₄(tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, BARF), B(C₆F₅)₄(tetrakis(pentafluorophenyl)borate), B(Ph)₄ (tetraphenylborate),Al(OC(CF₃)₃)₄, and CB₁₁H₁₂ (carborane anion).

The invention provides an organic charge transport material comprisingthe complex of the invention and/or a salt comprising the complex.

In the context of the present invention, the reference to a materialcomprising the complex of the invention generally encompasses, as apreferred embodiment, a material comprising a salt comprising thecomplex.

The “organic charge transport material” may also be referred to asorganic electron and/or hole transport material. The term “organic” maybe omitted, but generally, the charge transport material comprises anorganic compound. The “organic charge transport material” is an organicsemiconductor and/or conductor based on single molecules, oligomers,polymeric compounds and mixtures of the aforementioned. In the organiccharge transport material, charges are substantially transported byelectronic motion and/or charge hopping and not or only to aninsignificant extent by diffusion of charged molecules. Accordingly,this material may be an electron and/or hole conducting material. U.Bach et al. “Solid-state dye-sensitized mesoporous TiO₂ solar cells withhigh photon-to-electron conversion efficiencies”, Nature, Vol. 395, Oct.8, 1998, 583-585, disclose the amorphous organic hole transport material2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirofluorene(OMeTAD) in dye-sensitised solar cells. In WO2007/107961, chargetransporting materials, which are liquid at room temperature and theirapplication in dye-sensitized solar cells are disclosed (for example,tris(p-methoxyethoxyphenyl)amine (TMEPA)). These and other materials maybe used, for example, for the purpose of the present invention. Also EP1160888 A1 discloses an “organic electrically conducting agent”. The“organic charge transport material” thus has characteristics such as aconductivity, which is generally influenced by the presence or absenceof a dopant. Typical current carriers in organic semiconductors areholes and electrons in π-bonds. When organic molecules have π-conjugatesystems, electrons can move via π-electron cloud overlaps, especially byhopping, tunneling and related mechanisms. Polycyclic aromatichydrocarbons and phthalocyanine salt crystals are examples of this typeof organic semiconductor. In the context of the present invention, anionic liquid and a liquid electrolyte, in which charges are transportedby diffusion of molecules, are not considered as organic chargetransport material.

In the context of the invention, the complex (or a salt comprising thecomplex) of the invention is used to adjust, in particular increase theconductivity of an organic charge transporting material, and/to dope theorganic charge transport material. The complex (or salt) may also beused as a dopant in other types of conductors or semiconductors.

The complex or salt comprising the complex may also be used to adjustthe ionization potential and/or Fermi level of the organic chargetransport material.

The invention thus provides an organic charge transporting materialcomprising the complex of the invention. The complex may be added at aweight percentage of 0.001 to 10%, preferably 0.01 to 8%, morepreferably 0.1% to 5% and most preferably 0.5 to 4%, for example 1 to 3%or 1 to 2.5%, with respect to the weight of the organic chargetransporting material. Preferably, the weight percentages do not includeany solvent but refer directly and to the organic charge transportingmaterial.

The organic charge material comprising the complex of the inventionforms a doped organic charge transport material of the invention.

The complexes of the invention may be used as p-dopants and asn-dopants. For obtaining an n-dopant, the same complexes having the sameoverall structure as those used for p-dopants can be used. The onlydifference is that instead of using D+ complex in the D+/D redox couple,the D− in the D/D− redox couple has to be used. Such complexes can beprepared by shaking complex D with alkali metals (potassium or lithiumfor example). For example, complex 2 (FIG. 1) will generally be used asn-dopant. Complex 2 can be considered as D+ [Co(L)3)³⁺]. A complex withsame structure but charged as D−, for example [Co(L)3)+] can be used asn-dopant if E(D/D−)<E (reduction of the material to be doped). Inaddition, while Co3+, a d6 electron system, was used for p-doping, Co+,a d8 electron system could be used for n-doping. The complexes preparedcan be multiple electron donor. E.g. [Fe(bpy)3Na] or [Fe(bpy)3] areexpected to give 4 and 3 electrons respectively. A complexbis-terdentate would give 2 or 3 electrons. Methods of preparation aredisclosed in (1) Mahon, Carol; Reynolds, Warren Lind. Preparation ofsodium tris(2,2′-bipyridine)ferrate(—I). Inorganic Chemistry (1967),6(10), 1927-8. (2) Herzog, Siegfried; Weber, Albert. Alkali metaladducts of some neutral complexes of iron with bipyridine andbipyridine-like ligands. Zeitschrift fuer Chemie (1968), 8(2), 66.WO2005/036667 discloses an electrochemical method.

Reference is made to US 2005/0061232 and US 2010/0140566, whichillustrate the use of dopants in organic semiconductors.

The invention provides an electrochemical device comprising the complexof the invention. In particular, the complex is used as a redox-coupleand/or as a dopant in such devices, or in accordance with the other usesspecified elsewhere in this specification. Preferably, the inventionprovides an electrochemical device comprising an organic chargetransport material comprising the complex of the invention.

According to an embodiment, the invention provides an electrochemicaldevice, preferably a photoelectrochemical device comprising the complexof the invention.

According to an embodiment, the electrochemical device of the inventionis selected from a photovoltaic cell, a battery, a rechargeable battery(for example a lithium ion battery), a light emitting device, anelectrochromic device, a photo-electrochromic device, an electrochemicalsensor, a biosensor, an electrochemical display and an electrochemicalcapacitor, (for example a double layer capacitor and/or a supercapacitor).

According to an embodiment, the device is a battery, for example alithium ion battery. Complexes of the invention may, for example, beused as redox couples in such devices. The complexes of the inventionmay also or specifically as redox couples be used to preventover-charging and/or over-discharging in rechargeable batteries. Wang etal., “A new strategy of molecular overcharge protection shuttles forlithium ion batteries”, Electrochem. Commun., 10 (2008) 651-654discloses the use of redox-shuttle additives in the electrolyte orembedded in a separator between the electrolyte and an electrode, andtheir use for preventing over-charging and/or over-discharging of thedevices. The complexes of the invention may be used in the same way, asadditives to the electrolyte or in the separator, for example. As Wanget al. (2008) disclose, the oxidation potential of the redox couples iseither preferably higher than the redox potential of the cathodematerial (“p-type shuttle”), or lower than the material of the anodematerial (“n-type shuttle”). In these devices, the redox couple providean internal shunt, which prevents deterioration of the cell by imposinga limit on cell potential. The complexes of the invention may be used asboth, n- or p-type shuttles (see above: D+/D, D/D−)) in rechargeablebatteries, in particular lithium ion batteries. Further background withrespect to over-charge and over-discharge protection in lithium-ionbatteries is disclosed by S.-I. Nishimura et al. Nat. Mater., 7 (2008)707-711. C. Buhrmester, J. Electrochem. Soc. 153 (2) A288-A294 (2006).

According to an embodiment, the device of the invention is aphotoelectochemical device. The photoelectrochemical device may, forexample, may be selected from a dye sensitized solar cell (DSC), inparticular a solid state DSC (ssDSC), an electrochromic device, aphoto-electrochromic device and an organic light emitting diode (OLED)comprising the complex of the invention.

According to an embodiment, the device of the invention is an OLED. WO2005/036667 discloses OLEDs that comprise ruthenium complexes for dopingorganic semiconductors. The complexes of the invention may used in thesame manner. In particular, the complexes of the invention may also beused to increase charge mobility and/or charge density in organic chargetransporting materials, for example in organic semiconductors. Whileusing negatively charged ligands (e.g. La and Xb) in the complex of theinvention, neutral complexes may be obtained, which may be applied by anevaporation process as disclosed in WO 2005/036667. Doped layers may beproduces by mixed evaporation of a matrix (for example a chargetransporting material) and the dopant.

US 2006/0250076 discloses OLEDs comprising doped charge carriertransport layers. The complexes of the invention may thus be used inOLEDs, in particular as dopants in charge carrier transport layersand/or in layers comprising organic charge transport material.

Also

More preferably, the invention provides a dye-sensitized solar cell(DSC), most preferably a solid state dye-sensitized solar cell (ssDSC).According to an embodiment, the invention provides a solar cellcomprising a layer comprising a doped organic charge transport materialin accordance with the invention.

The electrochemical device of the invention, in particular the DSC ispreferably a regenerative device.

Electrochemical devices generally comprise two electrodes and one ormore layer between the electrodes. The electrochemical device of theinvention preferably comprises a layer comprising an organic chargetransport material and the complex of the invention.

In the figures, FIG. 14 schematically shows a dye-sensitized solar cell.

The device of the present invention comprises at least one substrate 1.Contrary to the device shown in FIG. 14, the present invention alsoencompasses devices having only one substrate 1, for example only a topor only a bottom substrate 1, as is shown more specifically in FIG. 16.Preferably, there is a substrate facing the side of the device intendedto be exposed to electromagnetic radiation for production of electricalcurrent. The substrate facing radiation is preferably transparent.Transparency, for the purpose of the present invention, generally meansthat the respective structure (for example substrate, counter electrode,conductive layer, porous semiconductor) is transparent to at least somevisible light, infrared light or UV light, in order to convert thislight to electrical energy in the device of the invention. Preferably,transparent means transparent to all visible light, more preferably alsoto some of the near infra-red and/or also to at least part of theultraviolet light spectrum.

The substrate 1 may be made from plastic or from glass. In flexibledevices, the substrate 1 is preferably made from plastic. In anembodiment, the substrate comprises a plastic selected from the groupsof polyethylene terephthalate, polyethylene naphthalate, polycarbonate,polypropylene, polyimide, 3-acetyl cellulose, and polyethersulfone, forexample.

The conversion devices of the present invention generally have twoconductive layers 2 and 7, wherein a first conductive layer 2 isrequired for removing the electrons generated from the device, and asecond conductive layer 7 for supplying new electrons, or, in otherwords, removing holes. This is illustrated in FIG. 16 by the signs + and−. The conductive layers 2 and 7 may be provided in many different formsand may be made from various materials, depending on the purpose ornature of the device.

The second conductive layer 7 may be part of the substrate 1, as is thecase, for example with ITO (indium tin oxide)-coated plastic or glass,where the transparent ITO is coated on the plastic or glass and makesthe later electrically conductive.

Accordingly, one or both conductive layers 2 and 7 may comprise atransparent metal oxide, such as indium doped tin oxide (ITO), fluorinedoped tinoxide (FTO), ZnO—Ga₂O₃, ZnO—Al₂O₃, tin-oxide, antimony dopedtin oxide (ATO) and zinc oxide.

According to embodiments of the invention, only the first conductivelayer 2 or only the second conductive layer 7 comprises a transparentmetal oxide layer as defined above. It is also possible to provide oneor both of the two opposed conductive layers 2 and 7 in the form of aconductive foil, for example a metal foil, in particular a titanium foilor zinc foil. This is preferred, for example, in some flexible devices,as detailed below. Preferably, the first conductive layer 2, is madefrom a conductive metal foil, for example, as is shown in FIG. 16. Sucha foil may not be transparent.

The device of the present invention generally comprises a counterelectrode 7, which faces an intermediate layer 6 towards the inside ofthe cell, and the substrate 1 on the outside of the cell, if suchsubstrate is present. The counter electrode generally comprises acatalytically active material, suitable to provide electrons and/or fillholes towards the inside of the device. The counter electrode may thuscomprises materials selected from material selected from Pt, Au, Ni, Cu,Ag, In, Ru, Pd, Rh, Ir, Os, C, conductive polymer and a combination oftwo or more of the aforementioned, for example. Conductive polymers maybe selected from polymers comprising polyaniline, polypyrrole,polythiophene, polybenzene and acetylene, for example.

In FIG. 14, the second conductive layer can be considered as part of thecounter electrode 7 or as part of the substrate 1 on the top of thedevice, and is thus not separately shown. If the second conductive layeris considered to be part of the substrate 1, such substrate could beplastic or glass coated with ITO or other materials, as mentioned above,for example.

In FIG. 14, layer 3 is a light absorption layer, which comprisesactually at least two separate layers, namely a porous semiconductorlayer 4 and, absorbed thereon, a sensitizer layer 5. The sensitizerlayer may comprise one or more of the group consisting of:organo-metallic sensitizing compounds, metal free organic sensitizingcompounds, inorganic sensitizing compounds such as quantum dots, Sb2S3(Antimonysulfide, for example in the form of thin films), andcombinations of the aforementioned.

The sensitizer may, for example, comprise sensitising dyes 5. If thesensitizer layer 5 comprises a dye, it generally comprises, besidesoptional co-adsorbed compounds, such as those disclosed inWO2004/097871A1, for example, at least one dye or sensitizer, or acombination of two or more different sensitizers. Examples fororganometallic compounds encompass ruthenium dyes, as they are currentlyused in such devices. Suitable ruthenium dyes are disclosed, forexample, in WO2006/010290.

The dye layer may comprise organic sensitizers. For example, the devicemay be free of any sensitizer using ruthenium or another noble metal.

The porous semiconductor layer may be produced by processes described inthe art (B. O'Reagan and M. Grätzel, Nature, 1991, 353, 373) fromsemiconductor nanoparticles, in particular nanocrystalline particles.Such particles generally have a mean diameter of about 0-50 nm, forexample 5-50 nm. Such nanoparticles may be made from a material selectedfrom the group of Si, TiO₂, SnO₂, ZnO, WO₃, Nb₂O₅ and TiSrO₃, forexample. The constitution of the porous layers from nanocrystallineparticles is clearly visible in the schematic FIG. 16, showing anembodiment of a flexible cell according to the invention.

The device of the present invention has a layer 6 having the generalpurpose of mediating the regeneration of electrons in the dye, whichwere removed due to radiation. These electrons are provided by thecounter electrode 7, and layer 6 thus mediates the transport ofelectrons from the counter electrode to the dye, or of holes from thedye to the counter electrode. The transport of electrons and/or holes ispreferably mediated by electrically conductive materials. Accordingly,the layer 6 is preferably an organic charge transport layer.

According to a preferred embodiment of the invention, this intermediate(or organic charge transport) layer 6 is substantially free of asolvent. This embodiment is particularly relevant with respect toflexible devices. Substantially free means, for the purpose of thepresent invention, that the layer comprises less than 10% by weight,more preferably less than 5 wt. %, even more preferably less than 1% andmost none added solvent at all. In contrary to many prior art devicesand in particular to flexible devices made from polymers, the fact thatthe intermediate layer is solvent free provides the important advantagethat there is no degradation due to solvent evaporation through the oneor two substrate layer(s) 1.

According to an embodiment, the organic charge transport layer 6comprises an organic charge transport material and the complex of theinvention.

According to an embodiment, the device of the present inventioncomprises at least one substrate layer 1, a conductive layer 2, a lightabsorption layer 3, a doped organic charge transport material layer 6,and a counter electrode 7, wherein said conductive layer 2, said lightabsorption layer 3, said organic charge transport layer 6 and saidcounter electrode 7 are connected in series. According to a preferredembodiment, the device comprises two transparent substrates 1, on thetop and the bottom of the device, respectively. The top of the devicecorresponds to the top of the drawing in FIG. 14. The top corresponds tothe side where the major part of light enters the device. Theintermediate layer 6 comprises an organic charge transporting materialcomprising the complex of the invention and is provided between the dyelayer 5 and the counter electrode 7.

According to another embodiment, the device of the present invention isa flexible device. Preferably, according to this embodiment, the devicecomprises a flexible substrate 1, a counter electrode 7, a chargetransport layer 6, a dye layer 5, which may comprise organometallicdyes, organic dyes, or both, a porous semiconductor layer 4, and aconductive layer 2. Preferably, said layers are connected in series, forexample in that order from the top to bottom.

Preferably, in the flexible device, the said conductive layer 2 isprovided by a conductive metal foil, such as a titanium or zinc foil, asshown by reference numeral 2 in FIG. 5, for example, and said flexiblesubstrate 1 is a polymer or plastic foil. A second conductive layer,which is transparent, is part of the counter electrode 7 and is incontact with the plastic foil as described above (for example in theform of ITO-PET or ITO-PEN). Conductive titanium foils and conductiveplastic substrates are disclosed by Seigo Ito et al. Chem. Comm. 2006,4004-4006, and in EP1095387, for example.

According to an embodiment, the flexible device of the present inventionis an inversed solar cell, with electromagnetic radiation entering thecell mainly from the side of the counter electrode (back illumination),as shown in FIG. 16, where the arrow hv refers to the side ofillumination.

According to an embodiment, the flexible cell of the present inventionis an inversed solar cell, in which, a transparent plastic substrate 1comprises a counter electrode assembly 7, which, in this order from topto the bottom, comprises a transparent conductive oxide, for example ITO(tin-doped indium oxide) deposited on the flexible plastic foil 1, and acatalyst, such as carbon or Pt (platinum), for example.

On the bottom end, a conductive foil 2, preferably a metal foil, such asa Ti or zinc foil, for example, is provided, which may but need not beprovided on a flexible support, such as a plastic material.

EXAMPLES Example 1 Synthesis of Different Pyridine-Pyrazole Ligands

2-(1H-pyrazol-1-yl)pyridine (also 1-(pyridine-2-yl)-1H-pyrazol, Py-Pz))(see ligands of complex 1 in FIG. 1) was obtained as disclosed inElguero J. et al., Chemische Berichte, 1996, 129, pages 589-594.

4-Methyl-2-(1H-pyrazol-1-yl)pyridine (MePy-Pz). 0.95 g (14.0 mmol, 2 eq)of Pyrazole was dissolved in 20 mL of DMSO at room temperature and 1.57g (14.0 mmol, 2 eq) of KO^(t)Bu was added. The mixture was heated to 40°C. for 20 min. and then 0.78 g (7.0 mmol, 1 eq) of 2-Fluoro-4-picoline(2-Fluoro-4-methyl-pyridine) was added and the mixture was heated to110° C. overnight. After cooling to room temperature the mixture wasdiluted with water and extracted with Et₂O (3×). The combined colourlessorganic layers were washed with water, dried over MgSO₄ andconcentrated. The yellow oil was purified by column chromatography usingCH₂Cl₂/EtOAc=6/1 as solvent mixture. The pure product was obtained ascolourless liquid in 99% yield (1.11 g, 6.9 mmol).

2-(3,5-Dimethyl-1H-pyrazol-1-yl)pyridine (Py-PzMe₂) and2-(3,5-Dimethyl-1H-pyrazol-1-yl)-4-methylpyridine (MePy-PzMe₂) weresynthesized accordingly.

4,4′-Dichloro-2,2′-bipyridine (CAS-No. 1762-41-0, also referred to asCl₂Bipy herein) is commercially available.

Example 2 Synthesis of [Co(Py-Pz)₃](PF₆)₂ (CoIII Complex 1)

225 mg (1.55 mmol, 3.1 eq) of pyridine-pyrazole (Py-Pz) ligand(Example 1) were dissolved in 20 mL of MeOH and then 119 mg (0.5 mmol, 1eq) of CoCl₂*6H₂O were added as a solid. The mixture was heated toreflux for 2 h. After cooling to r. t. excess of KPF₆ dissolved in MeOHwas added to the mixture. The mixture was stored at 3° C. forprecipitation. After 3 h the product was collected on a sintered glassfrit and dried in vacuo. The pure product (FIG. 1, compound 1) wasobtained as orange crystals. Yield: 246 mg (0.33 mmol, 66%). HRMS(ESI-TOF) m/z (%): calcd. for C₂₄H₂₁CoN₉. 247.0626. found 247.0635 (100)[(M-2 PF₆)²⁺].

Example 3 Synthesis of [Co(Py-Pz)₃](PF₆)₃ (CoIII Complex 2)

218 mg (1.5 mmol, 3.0 eq) of pyridine-pyrazole ligand were dissolved in10 mL of water and heated to 75° C. until complete solution occurred.Then 119 mg (0.5 mmol, 1 eq) of CoCl₂*6H₂O were added to the colourlesssolution. To the pink solution H₂O₂ (1 mL, 30%) and HCl (1 mL, 25%) wereadded to oxidize the cobalt. After 10 min. 460 mg (2.5 mmol, 5 eq) ofKPF₆ dissolved in 10 mL of hot water were added drop wise to themixture. Precipitation occurred and the mixture was allowed to cool toroom temperature. The product was collected on a sintered glass frit anddried in vacuo. The pure fac-Isomer (FIG. 1, complex 2) was obtained asorange solid. Yield: 259 mg (0.28 mmol, 56%). ¹H NMR (400 MHz,acetone-D6): δ 9.56-9.53 (m, 3H, ArH), 8.73-8.64 (m, 6H, ArH), 8.01-7.81(m, 9H, ArH), 7.27-7.23 (m, 3H, ArH) ppm.

Examples 4 and 5 Synthesis of [Co(MePy-Pz)₃](PF₆)₂, and[Co(p-MePy-Pz)₃](PF₆)₃ (CoII and CoIII Complexes 3 and 4)

478 mg (3.0 mmol, 3.0 eq) of MePy-Pz ligand (Example 1) were dissolvedin a 2:1 mixture of water and MeOH (20 mL/10 mL) and then heated to 70°C. 238 mg (1.0 mmol, 1 eq) of CoCl₂*6H₂O were added as a solid. Themixture was stirred at 70° C. for 10 min and then 0.92 g KPF₆ dissolvedin 20 mL of hot water were added. After cooling to r. t. the precipitatewas collected on a sintered glass frit, washed with water and Et₂O anddried in vacuo. The pure fac-Isomer (FIG. 1, complex 3) was obtained aspale orange solid. Yield: 668 mg (0.81 mmol, 81%). HRMS (ESI-TOF) m/z(%): calcd. for C₂₇H₂₇CoN₉. 268.0861. found 268.0860 (100) [(M-2PF₆)²⁺]. Anal. Calcd. for C₂₇H₂₇CoF₁₂N₉P₂ (826.43): C, 39.24; H, 3.23;N, 15.25. found: C, 39.23; H, 3.35; N, 14.84%.

380 mg (2.4 mmol, 3.0 eq) of MePy-Pz ligand were dissolved in a 2:1mixture of water and MeOH (20 mL/10 mL) and then heated to 70° C. 190 mg(0.8 mmol, 1 eq) of CoCl₂*6H₂O were added as a solid. The mixture wasstirred at 70° C. for 10 min and then 2 mL of H₂O₂ (30%) and 2 mL of HCl(25%) were added and the mixture was stirred at 70° C. for further 30min. 0.92 g KPF₆ dissolved in 20 mL of hot water were added. Aftercooling to r. t. the precipitate was collected on a sintered glass frit,washed with water and Et₂O and dried in vacuo. The pure fac-Isomer (FIG.1, complex 4) was obtained as orange solid. Yield: 287 mg (0.3 mmol,38%). ¹H NMR (400 MHz, acetone-D6): δ 9.49-9.46 (m, 3H, ArH), 8.56 (s,3H, ArH), 7.94 (d, J=30.2 Hz, 3H, ArH), 7.73-7.71 (m, 3H, ArH),7.68-7.60 (m, 3H, ArH), 7.25-7.21 (m, 3H, ArH), 2.73 (s, 9H, CH₃) ppm.HRMS (ESI-TOF) m/z (%): calcd. for C₂₇H₂₇CoN₉P₂F₁₂ 826.1005. found826.1021 (35) [(M-PF₆)⁺]. calcd. for C₂₇H₂₇CoN₉PF₆ 340.5682. found340.5704 (63) [(M-2 PF₆)²⁺].

Examples 6 and 7 Synthesis of [Co(Py-PzMe₂)₃](PF₆)₂, and [Co(Py-PzMe₂)₃](PF₆)₃ (CoII and CoIII Complexes 5 and 6)

520 mg (3.0 mmol, 3.0 eq) of Py-PzMe₂ ligand (Example 1) were dissolvedin a 2:1 mixture of water and MeOH (20 mL/10 mL) and then heated to 70°C. 238 mg (1.0 mmol, 1 eq) of CoCl₂*6H₂O were added as a solid. Themixture was stirred at 70° C. for 10 min and then 0.92 g KPF₆ dissolvedin 20 mL of hot water were added. After cooling to r. t. the precipitatewas collected on a sintered glass frit, washed with water and Et₂O anddried in vacuo. The pure product (pink solid) (FIG. 1, complex 5) wasobtained as mixture of mer- and fac-Isomer. Yield: 737 mg (0.85 mmol,85%). HRMS (ESI-TOF) m/z (%): calcd for C₃₀H₃₁CoN₉. 289.1096. found289.1091 (100) [(M+2H-2 PF₆)²⁺]. Anal. Calcd. for C₃₀H₃₃CoF₁₂N₉P₂(868.51): C, 41.49; H, 3.83; N, 14.51. found: C, 40.69; H, 3.86; N,13.56%.

1.04 g (6.0 mmol, 3.0 eq) of Py-PzMe₂ ligand were dissolved in a 2:1mixture of water and MeOH (40 mL/20 mL) and then heated to 70° C. 476 mg(2.0 mmol, 1 eq) of CoCl₂*6H₂O were added as a solid. The mixture wasstirred at 70° C. for 10 min and then 5 mL of H₂O₂ (30%) and 5 mL of HCl(37%) were added and the mixture was stirred at 70° C. for further 3 h.Excess of aq. KPF₆ solution was added. After cooling to r. t. theprecipitate was collected on a sintered glass frit, washed with waterand Et₂O and dried in vacuo. The pure product (FIG. 1, complex 6) wasobtained as orange solid. Yield: 100 mg (0.1 mmol, 5%). ¹⁹F NMR (188MHz, acetone-D6): δ −72.6 (d, ¹J_(PF)=706 Hz, PF₆) ppm. HRMS (ESI-TOF)m/z (%): calcd. for C₃₀H₃₃CoN₉P₂F₁₂ 868.1475. found 868.1669 (100)[(M-PF₆)⁺].

Examples 8 and 9 Synthesis of [Co(Cl₂Bipy)₃](PF₆)₂, and[Co(Cl₂Bipy)₃](PF₆)₃ (CoII and CoIII Complexes 7 and 8)

238 mg (1.0 mmol, 1 eq) of CoCl₂*6H₂O were dissolved in 15 mL of waterand 675 mg (3.0 mmol, 3 eq) of 4,4′-Dichloro-2,2″-bipyridine (Cl₂Bipy,Example 1), dissolved in 50 mL of acetone, were added. The solutioninstantly turned orange and was heated to 50° C. for 10 min. The mixturewas concentrated until precipitation occurred. Then the mixture washeated to 50° C. again and just enough acetone was added to re-dissolvethe precipitate. Excess of saturated aq. KPF6 solution was added toprecipitate the complex as its PF₆ salt. The solid was collected on aglass-frit, washed with water and Et₂O and dried on air at 90° C. andthen in vacuo. The product (FIG. 1, complex 7) was obtained as beigesolid. Yield: 950 mg (0.93 mmol, 93%). ¹H NMR (400 MHz, acetone-D6): δ90.11 (s, 6H, ArH), 80.97 (s, 6H, ArH), 42.25 (s, 6H, ArH) ppm. ¹⁹F NMR(188 MHz, acetone-D6): 8-73.8 (d, ¹J_(PF)=706 Hz, PF₆) ppm. Anal. Calcd.for C₃₀H₁₈Cl₆CoF₁₂N₆P₂ (1224.08): C, 35.18; H, 1.77; N, 8.21. found: C,36.58; H, 1.76; N, 8.25%.

238 mg (1.0 mmol, 1 eq) of CoCl₂*6H₂O were dissolved in 15 mL of waterand 675 mg (3.0 mmol, 3 eq) of Cl₂Bipy, dissolved in 60 mL ofacetonitrile, were added. The solution instantly turned orange and washeated to 50° C. for 10 min. About 15 mL of acetonitrile were removed invacuo. Then 4 mL of H₂O₂ (30%) and 4 mL of HCl (25%) were added. Themixture was heated to 50° C. for 90 min. Excess of saturated aq. KPF₆solution was added to precipitate the complex as its PF₆ salt. The solidwas collected on a glass-fit, washed with water and Et₂O and dried invacuo. The product (FIG. 1, complex 8) was obtained as pale green solid.Yield: 1.125 g (0.96 mmol, 96%). ¹H NMR (400 MHz, acetone-D6): δ 9.30(t, ⁴J_(HH)=1.3 Hz, 6H, ArH), 7.97 (d, ⁴J_(HH)=1.3 Hz, 12H, ArH) ppm.¹⁹F NMR (188 MHz, acetone-D): δ −72.3 (d, ¹J_(PF)=708 Hz, PF₆) ppm. HRMS(ESI-TOF) m/z (%): calcd. for C₃₀H₁₈Cl₆CoF₆N₆P 438.9336. found 438.9354(45) [(M-2 PF₆)²⁺]. calcd. for C₃₀H₁₈Cl₆CoN₆ 244.3010. found 244.3019(100) [(M-3 PF₆)³⁺]. Anal. Calcd. for C₃₀H₁₈Cl₆CoF₁₈N₆P₃ (1169.05): C,30.82; H, 1.55; N, 7.19. found: C, 31.04; H, 1.35; N, 7.35%.

Example 10 Redox Potential, Choice of Dopant and ConductivityMeasurements

For conductivity measurements, substrates used for two-probe electricalconductivity measurements consisted of highly doped Si with a 300 nmthermally grown SiO₂ layer on which 5 nm Cr/30 nm Au electrodes weredeposited and lithographically patterned to yield a channel length andwidth of 20 μm and 1 mm, respectively. As a cleaning step, thesubstrates were sonicated in acetone and subsequently rinsed with2-propanol, followed by the removal of residual organic traces viaoxygen plasma treatment. The hole conductor was subsequently depositedby spin-coating a solution of Spiro-MeOTAD, TBP, LiTFSI and complex 2 inCHCl₃, whereas the concentrations were the same as in case ofphotovoltaic devices. I-V characteristics were recorded on a Keithley4200 Semiconductor Characterization System.

The oxidation potential of spiro-MeOTAD in solution has been found to be0.81 V versus normal hydrogen electrode (NHE) (Moon, S. et al. J. Phys.Chem. C 2009, 113, 16816-16820.) The basic requirement for theCo^((III)) (complex thus is a redox potential lying above this value.For this reason we selected cobalt(III)tris(1-(pyridin-2-yl)-1H-pyrazol)denoted complex 2 and depicted in FIG. 1, as suitable candidate forp-type doping of Spiro-MeOTAD.

Complex 2 has a redox potential of 0.95 V vs. NHE as determined byelectrochemical measurements, which leaves a sufficient driving force ofroughly 150 mV for the charge transfer reaction. Complex 2 and itsCo^((II)) analog have almost no absorption in the visible region, whichis an advantage in DSCs, because competition with the sensitizer forlight harvesting in avoided.

The basic mechanism of p-type doping is the creation of additionalcharge carriers (holes), leading to an increased charge carrier densityin and therefore higher conductivity of the semiconductor film. Thiscorresponds to results obtained from two-probe conductivity measurementsshowing an increase in conductivity from 4.4×10⁻⁵ to 5.3×10⁻⁴ ⁵ cm⁻¹upon the addition of 1.0% complex 2. Snaith et al. (Appl. Phys. Lett.2006, 89, 262114) previously reported a conductivity of 2.0×10⁻⁵ S cm⁻¹for the undoped Spiro-MeOTAD, a value that is in agreement with ourfindings, taking into account that a slightly different concentration ofLiTFSI has been used. For higher doping concentrations, the conductivityincreases exponentially with the doping ratio as shown in FIGS. 2 and 3.It has to be noted that given doping ratios correspond to the molarpercentage of complex 2 that has been added to the Spiro-MeOTAD solutionprior to spin-coating, but not necessarily to the resulting dopingconcentration within the amorphous film. This experiments show thatcomplex 2 effectively dopes Spiro-MeOTAD.

Example 10 Preparation of a Solid State Dye-Sensitized Solar Cell

First, fluorine-doped tin-oxide (FTO) coated glass substrates (Tec15,Pilkington) were patterned by etching with zinc powder and 2 Mhydrochloric acid. After cleaning, a TiO₂ compact layer was deposited onthe substrates by aerosol spray pyrolysis at 450° C. using titaniumdiisopropoxide bis(acetylacetonate) dissolved in ethanol (1:10, volumeratio) as precursor and oxygen as carrier gas. After cooling to roomtemperature the substrates were treated in an 0.02 M aqueous solution ofTiCl₄ for 30 min at 70° C., rinsed with deionized water and dried at450° C. during 15 min. A 2.5 m thick mesoporous TiO₂ layer composed of20 nm sized particles was then deposited on the substrates by ascreen-printing technique, dried at 125° C., gradually heated to 500° C.and then baked at this temperature for 15 min. The aforementionedtreatment in aqueous TiCl₄ solution was repeated and the substratesagain dried at 450° C. during 15 min. Prior to sensitization the TiO₂substrates were heated to 500° C. during 30 min. After cooling toapproximately 70° C. the substrates were immersed into a 10⁴ M solutionof the Y123 sensitizer (Tsao et al., ChemSusChem 2011, 4, 591-594) in amixture of acetonitrile and tert-butyl alcohol (1:1, volume ratio) for 1h. The hole-transporting material was deposited by spin-coating at 2000rpm for 30 s. The formulation of the spin-coating solution was 0.15 M(2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene)(Spiro-MeOTAD), 0.02 M Lithium bis(trifluoromethylsulfonyl)imide(LiTFSI) and 0.12 M 4-tert-butylpyridine (TBP) in chlorobenzene. When achemical dopant was used, it was pre-dissolved in acetonitrile and addedto the Spiro-MeOTAD solution prior to spin-coating.

In particular, three different doping ratios of 1.0%, 1.6% and 2.2% wereinvestigated comparing them to an undoped reference (Blank).

Finally 200 nm of silver were thermally evaporated on top of the deviceto form the back contact. The devices were sealed using a 25 m thickpolymer spacer (Surlyn, DuPont) and a microscopic cover slide.

Example 12 Device Characterization

Current-Voltage-Characteristics were recorded by applying an externalpotential bias to the cell while recording the generated photocurrentwith a Keithley model 2400 digital source meter. The light source was a450 W xenon lamp (Oriel) equipped with a Schott K113 Tempax sunlightfilter (Praezisions Glas & Optik GmbH) in order to match the emissionspectrum of the lamp to the AM 1.5 G standard (100 mW cm⁻²). Incidentphoton-to-electron conversion efficiency (IPCE) spectra were recordedwith a Keithley 2400 Source meter (Keithley) as function of wavelengthunder a constant white light bias of approximately 5 mW/cm² supplied bya white LED array. The excitation beam coming from a 300 W xenon lamp(ILC Technology) was focused through a Gemini-180 double monochromator(Jobin Yvon Ltd.) and chopped at approximately 4 Hz.

J-V characteristics measured under simulated AM1.5G solar irradiance(100 mW cm⁻²) are represented in FIG. 4 and the extracted photovoltaicparameters summarized in Table 1 below.

TABLE 1 Photovoltaic parameters derived from J-V measurements fordevices containing different doping ratios of complex 2 and an undopedreference (Blank). Blank 1.0% 1.6% 2.2% Initial 10 V_(oc) (mV) 808 846845 846 Data mW cm⁻² J_(sc) (mA cm⁻²) 1.0 1.0 1.0 0.9 FF 0.66 0.75 0.770.77 η (%) 5.8 6.8 7.2 6.5 100 V_(oc) (mV) 878 923 934 940 mW cm⁻²J_(sc) (mA cm⁻²) 9.1 10.2 10.4 9.6 FF 0.29 0.46 0.55 0.62 η (%) 2.3 4.35.3 5.6 After 100 V_(oc) (mV) 887 925 943 947 5 d mW cm⁻² J_(sc) (mAcm⁻²) 9.9 10.3 10.2 9.8 FF 0.30 0.54 0.63 0.65 η (%) 2.6 5.2 6.1 6.1

For the undoped reference we find an open-circuit potential V_(OC),short-circuit current density J_(SC) and fill factor FF of 878 mV, 9.1mA cm⁻² and 0.29, respectively, yielding an overall PCE η of 2.3%. Thisdevice suffers from a relatively poor fill factor that can be attributedto the low conductivity and therefore high charge-transport resistanceof the undoped spiro-MeOTAD film contributing to a high seriesresistance. Upon the addition of 1.0%, 1.6% and 2.2% of complex 2, thefill factor improves to 0.46, 0.55 and 0.62, respectively, resulting inpower conversion efficiencies of 4.3%, 5.3% and 5.6%. Concerning thephoto current density, the addition of FK102 leads to an increase ofJ_(SC) to 10.2 mA cm² (1.0% FK102) and 10.4 mA cm⁻² (1.6% FK102) and asubsequent decrease to 9.6 mA cm⁻² (2.2% FK102) at higher doping ratios.This decrease may be linked to a loss of current generation, as theoxidized species of Spiro-MeOTAD strongly absorb at 520 nm (ε=4.01×10⁴mol⁻¹ cm⁻¹) and therefore compete with the sensitizer for lightharvesting.

The open-circuit potential increases to 923 mV upon the addition of 1.0%complex 2 and surprisingly further increases to 934 and 940 mV when thedoping ratio is raised to 1.6% and 2.2%, respectively. This may be dueto a lowering of the Fermi level in the Spiro-MeOTAD film when thedopant is added, expanding the gap to the TiO₂ conduction band andtherefore the maximum potential difference theoretically achievable.Moreover, a higher conductivity facilitates charge extraction andconsequently obviates the accumulation of holes near the sensitizedjunction.

At full sunlight intensity (100 mW cm⁻²) a maximum power conversionefficiency of 5.6% is achieved for the device containing 2.2% of complex2. It is interesting to note that at low light intensity (10 mW cm⁻²)the maximum is reached for a doping ratio of 1.6% yielding a remarkablePCE of 7.2% (Table 1).

In general we observe that the power conversion efficiency of solarcells based on the aforementioned system significantly increases overtime when the devices are stored under dark. The comparison between J-Vdata measured several days after cell fabrication and the photovoltaicparameters initially obtained, reveals that this performance boostmainly results from an increase in FF (Table 1).

Devices based on the system presented herein generally reach powerconversion efficiencies between 6-7% measured 1-2 weeks after theirfabrication. For a champion device containing 1.6% of complex 2 dopantwe achieved an unprecedented power conversion efficiency of 7.2%measured under simulated AM1.5G solar irradiance (100 mW cm⁻²) (FIG. 5).To the best of our knowledge, this is the first time that such a highPCE has been obtained for an all solid-state dye-sensitized solar cell.For this device, we derive photovoltaic parameters V_(OC), J_(SC), andFF of 986 mV, 9.5 mA cm⁻² and 0.76, respectively, the corresponding J-Vcharacteristics are illustrated in FIG. 4.

In conclusion we have shown that chemical p-type doping is an effectivetool to tune the charge transport properties of spiro-MeOTAD insolid-state DSCs and capable of replacing commonly employedphoto-doping. Preliminary studies demonstrate that the reportedCo^((III)) complex (complex 2) fulfils the necessary requirements forthis kind of application and promising results could have been achieved.

The invention claimed is:
 1. A complex of formula (I):M(La)_(n)(Xb)_(m)  (I) being a dopant, wherein: M is a metal selectedfrom Co; n is an integer from 1 to 6 and a is a consecutive number of afirst set consisting of the integers of 1 to n (1, . . . , n), so thatthere are n ligands L1, . . . , Ln; m is 0 or an integer from 1 to 5 andb is a consecutive number of a second set consisting of 0 and integersof 1 to m (0, . . . , m), so that if m>0 there are m ligands X1, . . . ,Xm; wherein n and m equal the appropriate number of ligands present onmetal M; wherein any La (L1, . . . , Ln) is independently selected froma mono-, bi-, or tridentate ligand, with the proviso that at least oneof said ligands La (L1, . . . , Ln) is, independently, selected fromcompounds of formulae (1-3) to (3-3) below:

wherein, said ligand comprises at least one substituent R¹, R⁵, and/orR⁸, as applicable, being selected independently from the substituent(A-1) to (G-2) below:

wherein: the dotted line represents the bond connecting the substituentof (A-1) to (G-2)) on the compound of formula (1-3), (2-3) or (3-3);and, substituents R₁, R₂, R₃, R₄, R₅, and R₆, in as far as present, areindependently selected from H, halogen, —NO₂, —OH, —NH₂, and fromhydrocarbons comprising 1 to 30 carbons and 0 to 15 heteroatoms; R′ ofsubstituents (B-10), (C-9), (C-12), (C-14), and (C-16) is selected fromC1-C5 alkyl; wherein at least 3 ligands La are of identical structure(L1=L2=L3); and Xb is a monodentate co-ligand independently selectedfrom H₂O, Cl⁻, Br⁻, I⁻, CN, NCO, NCS, NCSe, NH₃, NR₇R₈R₉, and PR₇R₈R₉,wherein R₇, R₈, and R₉ are selected independently from substituted orunsubstituted alkyl, alkenyl, alkynyl and aryl.
 2. The complex accordingto claim 1, wherein n is 3 (M L1 L2 L3) and m is
 0. 3. The complexaccording to claim 1, which is cationic.
 4. The complex according toclaim 3, which is provided together with a suitable anionic speciesselected from the group consisting of halogen (Cl⁻, Br⁻, F⁻), CN⁻, NCO⁻,NCS⁻, NCSe⁻, ClO₄ ⁻ (perchlorate), PF₆ (hexafluorophosphate), BF₄(tetrafluoroborate), B(CN)₄ (tetracyanoborate), CF₃SO₃(trifluoromethanesulfonate, triflate), (CF₃SO₂)₂N(Bis(trifluoromethane)sulfonamide, TFSI), B(C₆H₃(m-CF₃)₂)₄(tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, BARF), B(C₆F₅)₄(tetrakis(pentafluorophenyl)borate), B(Ph)₄ (tetraphenylborate),Al(OC(CF₃)₃)₄, and CB₁₁H₁₂ (carborane anion).
 5. A complex of formula(I):M(La)_(n)(Xb)_(m)  (I) being a dopant, wherein: M is a metal selectedfrom Co; n is an integer from 1 to 6 and a is a consecutive number of afirst set consisting of the integers of 1 to n (1, . . . , n), so thatthere are n ligands L1, . . . , Ln; m is 0 or an integer from 1 to 5 andb is a consecutive number of a second set consisting of 0 and integersof 1 to m (0, . . . , m), so that if m>0 there are m ligands X1, . . . ,Xm; wherein n and m equal the appropriate number of ligands present onmetal M; wherein any La (L1, . . . , Ln) is independently selected froma mono-, bi-, or tridentate ligand, with the proviso that at least oneof said ligands La (L1, . . . , Ln) is, independently, selected fromcompounds of formulae (1-3) to (3-3) below:

wherein, said ligand comprises at least one substituent R¹, R⁵, and/orR⁸, as applicable, being selected independently from the substituent(A-1) to (G-2) below:

wherein: the dotted line represents the bond connecting the substituentof (A-1) to (G-2)) on the compound of formula (1-3), (2-3) or (3-3);and, substituents R₁, R₂, R₃, R₄, R₅, and R₆, in as far as present, areindependently selected from H, halogen, —NO₂, —OH, —NH₂, and fromhydrocarbons comprising 1 to 30 carbons and 0 to 15 heteroatoms; R′ ofsubstituents (B-10), (C-9), (C-12), (C-14), and (C-16) is selected fromC1-C5 alkyl; Xb is a monodentate co-ligand independently selected fromH₂O, Cl⁻, Br⁻, I⁻, CN, NCO, NCS, NCSe, NH₃, NR₇R₈R₉, and PR₇R₈R₉,wherein R₇, R₈, and R₉ are selected independently from substituted orunsubstituted alkyl, alkenyl, alkynyl and aryl; and wherein said complexof formula (I) is cationic.
 6. The complex according to claim 5, whereinn is 2 (M L1 L2) or 3 (M L1 L2 L3) and m is
 0. 7. The complex accordingto claim 5, which comprises at least 3 ligands La of identical structure(L1=L2=L3).
 8. The complex according to claim 5, which is providedtogether with a suitable anionic species selected from the groupconsisting of halogen (Cl⁻, Br⁻, I⁻), CN⁻, NCO⁻, NCS⁻, NCSe⁻, ClO₄ ⁻(perchlorate), PF₆ (hexafluorophosphate), BF₄ (tetrafluoroborate),B(CN)₄ (tetracyanoborate), CF₃SO₃ (trifluoromethanesulfonate, triflate),(CF₃SO₂)₂N (Bis(trifluoromethane)sulfonamide, TFSI), B(C₆H₃(m-CF₃)₂)₄(tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, BARF), B(C₆F₅)₄(tetrakis(pentafluorophenyl)borate), B(Ph)₄ (tetraphenylborate),Al(OC(CF₃)₃)₄, and CB₁₁H₁₂ (carborane anion).
 9. A complex of formula(I):M(La)_(n)(Xb)_(m)  (I) being a dopant, wherein: M is a metal selectedfrom Co; n is an integer from 1 to 6 and a is a consecutive number of afirst set consisting of the integers of 1 to n (1, . . . , n), so thatthere are n ligands L1, . . . , Ln; m is 0 or an integer from 1 to 5 andb is a consecutive number of a second set consisting of 0 and integersof 1 to m (0, m), so that if m>0 there are m ligands X1, . . . , Xm;wherein n and m equal the appropriate number of ligands present on metalM; wherein any La (L1, . . . , Ln) is independently selected from amono-, bi-, or tridentate ligand, with the proviso that at least one ofsaid ligands La (L1, . . . , Ln) is, independently, selected fromcompounds of formulae (1-3) to (3-3) below:

wherein, said ligand comprises at least one substituent R¹, R⁵, and/orR⁸, as applicable, being selected independently from the substituent(A-1) to (G-2) below:

wherein: the dotted line represents the bond connecting the substituentof (A-1) to (G-2)) on the compound of formula (1-3), (2-3) or (3-3);and, substituents R₁, R₂, R₃, R₄, R₅, and R₆, in as far as present, areindependently selected from H, halogen, —NO₂, —OH, —NH₂, and fromhydrocarbons comprising 1 to 30 carbons and 0 to 15 heteroatoms; R′ ofsubstituents (B-10), (C-9), (C-12), (C-14), and (C-16) is selected fromC1-C5 alkyl; Xb is a monodentate co-ligand independently selected fromH₂O, Cl⁻, Br⁻, I⁻, CN, NCO, NCS, NCSe, NH₃, NR₇R₈R₉, and PR₇R₈R₉,wherein R₇, R₈, and R₉ are selected independently from substituted orunsubstituted alkyl, alkenyl, alkynyl and aryl; and wherein said complexof formula (I) is cationic and is provided together with a suitableanionic species selected from the group consisting of halogen (Cl⁻, Br⁻,I⁻), CN⁻, NCO⁻, NCS⁻, NCSe⁻, ClO₄ ⁻ (perchlorate), PF₆(hexafluorophosphate), BF₄ (tetrafluoroborate), B(CN)₄(tetracyanoborate), CF₃SO₃ (trifluoromethanesulfonate, triflate),(CF₃SO₂)₂N (Bis(trifluoromethane)sulfonamide, TFSI), B(C₆H₃(m-CF₃)₂)₄(tetrakis[3, 5-bis(trifluoromethyl)phenyl]borate, BARF), B(C₆F₅)₄(tetrakis(pentafluorophenyl)borate), B(Ph)₄ (tetraphenylborate),Al(OC(CF₃)₃)₄, and CB₁₁H₁₂ (carborane anion).
 10. The complex accordingto claim 9, wherein n is 2 (M L1 L2) or 3 (M L1 L2 L3) and m is
 0. 11.The complex according to claim 9, which comprises at least 3 ligands Laof identical structure (L1=L2=L3).